Why Is My Heat Pump Not Working Properly?
Why Is My Heat Pump Not Working Properly?
Why Is My Heat Pump Not Working Properly?
Why Is My Heat Pump Not Working Properly?
Why Is My Heat Pump Not Working Properly?
UK Heat pump Help Technical Team
Independent Heat Pump Engineer
Why Is My Heat Pump Not Working Properly?
If your heat pump is running but the house stays cold, your hot water never quite reaches temperature, or your electricity bills are far higher than you expected, it rarely means the heat pump unit itself has failed. In the vast majority of cases we investigate, the problem is in how the system has been configured, designed, or commissioned and that is almost always fixable without replacing any hardware.
The frustrating reality is that many UK homeowners have already been told everything is “working normally” after an engineer visit, have paid for replacement parts that changed nothing, or have been left waiting for another call-out to the same problem. This guide walks through the most common heat pump problems we see, what is actually causing them, and where to start looking.
One important thing to understand before we go through each symptom: most of these problems are not exclusive to any single brand or model. A Vaillant, Mitsubishi, Samsung, Daikin, or NIBE system can all show the same issues if the underlying design or settings are wrong. The heat pump unit is usually the last place to look.
Common Signs Your Heat Pump Isn’t Working Properly
These are the most common experiences that bring UK homeowners to us for an independent review:
No heating — the system runs but the radiators or underfloor heating produce no useful warmth
No hot water — the cylinder never reaches a usable temperature or runs out quickly
Some rooms remain cold — the system heats well in part of the property but not all of it
Higher electricity bills than expected — the system is running but not efficiently
Constant on-and-off cycling — the system repeatedly starts and stops rather than running steadily
Fault codes appearing regularly — the same codes keep returning even after being reset
Low system pressure — the pressure gauge drops repeatedly and requires topping up
Loud or unusual noises — vibration, banging, persistent gurgling, or excessive humming
Heat pump running all day without reaching the set temperature — continuous operation with no result
Hot water running out — adequate volume one day, barely enough the next
For each of these, there is usually a specific, identifiable cause. And in most cases, it can be resolved without replacing the heat pump or calling out a specialist to site.
Your Heat Pump Runs Constantly
This is probably the single most common concern we hear from UK homeowners:
“My heat pump never seems to switch off is something wrong?”
Sometimes, no. Heat pumps are designed to run for long, steady periods at lower temperatures rather than in short intense bursts like a gas boiler. On a cold day, running for eight to twelve hours continuously is completely normal and is actually more efficient than cycling on and off. That is how the technology is meant to work.
The problem comes when the system runs all day and still cannot maintain the set temperature, or when electricity usage is noticeably higher than expected despite continuous operation. In those cases, continuous running is a symptom of something else:
Poor system balancing heat is not being distributed evenly, leaving some rooms without adequate flow
Low system flow rates restricted circulation preventing heat from reaching the furthest parts of the circuit
The House Never Feels Warm Enough
If the heating runs reliably and yet rooms still feel cold or never reach the temperature you have set, this is one of the most frequently investigated complaints we receive. The heat pump unit is usually working fine the issue lies in the heating circuit that surrounds it.
The four most common causes are:
Incorrect Flow Temperature
Heat pumps deliver heat gradually at lower water temperatures typically between 35°C and 50°C, compared to the 65–80°C a gas boiler produces. If the flow temperature target is set too low for your home’s heat demand, the radiators cannot release enough heat to warm the rooms, even if the system runs all day. This is one of the most commonly misunderstood settings issues we identify, and it is usually correctable without any hardware changes.
Poor Radiator Sizing
Radiators are rated for a specific heat output at boiler-level water temperatures. At heat pump flow temperatures, that same radiator produces roughly 40–50% of its rated output. If your radiators were sized for a gas boiler and never re-assessed for a heat pump, they may simply not have enough surface area to warm the rooms at lower temperatures regardless of how well the heat pump performs.
Closed TRVs
Thermostatic radiator valves reduce flow to a radiator once a room reaches temperature. If too many close at once, total system flow drops below what the heat pump needs triggering flow faults, short cycling, and reduced heating performance across the whole circuit. Using TRVs correctly with a heat pump is fundamentally different from how they were configured under a gas boiler, and settings carried over from a previous installation are often entirely wrong.
System Balancing Issues
In a correctly balanced system, each radiator receives roughly the flow rate it was designed for. When out of balance, radiators near the heat pump get too much flow while those further away receive too little some rooms are comfortable, others stay cold, regardless of how long the heating runs. Heat pump system balancing is rarely completed properly at commissioning and is one of the first things we check when a system is underperforming.
Your Electricity Bills Are Higher Than Expected
Higher-than-expected electricity use is one of the clearest signals that something in the system is not set up correctly and it is also one of the situations where the potential saving from getting the system properly configured is most tangible. We have worked with homeowners where a single settings change reduced electricity consumption by 20 to 30 per cent.
The most common drivers of high running costs are:
Excessive flow temperatures running at 55°C or above when the system should be targeting 40–45°C in most conditions
Weather compensation turned off or set incorrectly the system runs at the same high flow temperature in mild autumn weather as in midwinter
Constant short cycling the system starts and stops repeatedly rather than settling into a steady long run, which reduces efficiency significantly
Incorrect system design undersized emitters or poor pipework forcing higher-than-necessary flow temperatures just to achieve basic heating
Faulty controls a thermostat, zone valve, or controller causing the system to run when it should not
High running costs are almost always a system issue, not an inherent feature of heat pump technology. A well-configured system in a suitable property should cost less to run than a gas boiler not more. If yours feels expensive, the cause is worth finding.
Your Heat Pump Keeps Showing Fault Codes
Fault codes are the heat pump’s way of reporting that something is outside its expected operating parameters. The difficulty is that the code tells you what triggered it not why and the why is almost always more important than the code itself.
Some common examples of what is actually happening behind the code:
Communication faults often point to wiring issues or a damaged controller which may be unrelated to the original fault that preceded them
Temperature faults are frequently symptoms of wider problems incorrect flow temperature settings, inadequate emitters, or an oversized heat pump short cycling rather than running steadily
Resetting a fault code without establishing the cause means the same fault will almost certainly return sometimes within hours. The code is a starting point for diagnosis, not the diagnosis itself.
Your Heat Pump Keeps Losing Pressure
Recurring pressure loss is one of the most common issues we see and also one of the most frequently mismanaged, with many homeowners simply being told to top up the filling loop rather than actually fixing what is causing the drop. Repeatedly adding fresh water introduces oxygen into the closed system, which accelerates corrosion and creates further problems over time.
The most common underlying causes are:
Small water leaks often not visible as a drip; a weeping joint, valve seal, or slow-releasing connection is enough to gradually reduce pressure over days or weeks
Expansion vessel faults the vessel can no longer absorb thermal expansion, leading to pressure that builds rapidly when heating runs then falls again when the system cools
Automatic air vents passing small amounts of water alongside air during normal operation
Pressure relief valve discharging caused by the expansion vessel failing to manage thermal expansion correctly
Recent maintenance a single pressure drop after bleeding radiators is normal and usually just needs one top-up
The key distinction is whether the pressure drop is a one-off or a recurring pattern. If it keeps coming back within days or weeks, there is an underlying cause that should be identified and corrected.
Your Heat Pump Sounds Noisy
Some degree of noise from a heat pump is entirely normal, and many homeowners become concerned about sounds that are simply part of how the system operates. Understanding the difference between normal and abnormal noise saves a lot of unnecessary worry — and unnecessary call-outs.
Normal operational sounds you should expect:
Fan running the outdoor unit fan draws air through the heat exchanger and varies in speed throughout the day
Defrost cycles a rushing or hissing sound as the system briefly reverses to clear ice from the outdoor unit, typically lasting 5–15 minutes
Water circulation occasional flow sounds from pipework, particularly when the system first starts up
Refrigerant movement a quiet hiss or subtle bubbling as refrigerant moves through the indoor unit
Sounds that are worth investigating are those that are new, louder than before, or intermittent in a way you have not experienced previously. Persistent vibration, repeated banging when hot water finishes, gurgling in radiators that does not clear, or unusual electrical humming from the indoor unit can all point to genuine issues:
Air trapped in the system causing irregular heating in specific radiators and sometimes gurgling or knocking at the unit
Restricted flow conditions the system working against back pressure from a blocked filter, strainer, or partially closed valve
Loose mounting vibration transferring from the outdoor unit to a wall, bracket, or pipework
Circulation pump issues a pump that is failing, set to the wrong speed, or creating cavitation noise
Incorrect pipework undersized or unevenly routed runs creating turbulence and flow noise
Often the Problem Is Not the Heat Pump Itself
This is probably the most important thing to understand about heat pump problems in UK homes and the one most frequently overlooked by both homeowners and visiting engineers.
In a significant proportion of the systems we review, the heat pump unit is operating exactly as it should. The refrigerant cycle, the compressor, the temperature readings all within specification. The problems being experienced are caused by what surrounds the heat pump, not by the unit itself. The most common culprits are:
Control settings weather compensation curves, thermostat configuration, and schedule programming that does not suit the property
Cylinder configuration incorrect hot water timing, setpoint temperature, or immersion heater settings
Incorrect system design undersized emitters, wrong pipe routes, or missing components that were specified but never installed
Poor balancing uneven flow distribution that leaves some areas of the house consistently underheated
Blocked filters or dirty strainers reducing flow throughout the circuit and causing knock-on faults
Heating zones working against each other TRV settings or zone valve configurations creating conflicting demands that destabilise the system
This matters because the standard response to a heat pump that is not performing sending an engineer to inspect the unit often returns a “no fault found” result, because the unit itself is fine. The problem is in the system design and settings, and was never examined. Knowing this changes where you start looking.
How Do You Find Out What Is Actually Wrong?
Getting a reliable picture of what is wrong requires looking at the system as a whole not just running through fault codes or checking refrigerant pressure. Heat pumps rely on every connected part working correctly together, and a problem in one area routinely shows up as a symptom somewhere else entirely.
A proper diagnosis looks at all of these together:
The heat pump its operating data, fault history, current settings, and flow and return temperatures
Controls thermostat configuration, weather compensation curve, and schedule settings
Cylinder temperature target, timing, and whether the immersion heater is being used more than it should be
Circulation pumps speed settings and actual flow rate through the circuit
Pipework layout, sizing, insulation condition, and whether any restrictions are present
Radiators and emitters whether they are sized for heat pump flow temperatures, not boiler temperatures
Underfloor heating circuits flow rates, zone balancing, and whether manifold settings are correct
Weather compensation whether the heating curve is active, correctly set, and actually varying with outdoor temperature
When one part of this is incorrectly configured or was never set up properly at installation the symptom almost always shows up somewhere else. That is why a whole-system review consistently finds issues that individual fault-focused call-outs miss.
Need Help Identifying What Is Wrong With Your Heat Pump?
If your heat pump is not performing as expected whether that is a heating problem, a hot water issue, high electricity bills, or recurring fault codes our Fix My Heat Pump service provides independent technical support for homeowners across the UK. We look at the whole system, not just the unit.
We review your photographs, system data, settings, and fault history remotely giving you a specific, clear picture of what is causing the problem and what needs to change. Most heat pump performance issues have a resolution that does not require expensive parts, a manufacturer visit, or replacing the heat pump.
Why Is My Heat Pump Not Working Properly?
If your heat pump is running but the house stays cold, your hot water never quite reaches temperature, or your electricity bills are far higher than you expected, it rarely means the heat pump unit itself has failed. In the vast majority of cases we investigate, the problem is in how the system has been configured, designed, or commissioned and that is almost always fixable without replacing any hardware.
The frustrating reality is that many UK homeowners have already been told everything is “working normally” after an engineer visit, have paid for replacement parts that changed nothing, or have been left waiting for another call-out to the same problem. This guide walks through the most common heat pump problems we see, what is actually causing them, and where to start looking.
One important thing to understand before we go through each symptom: most of these problems are not exclusive to any single brand or model. A Vaillant, Mitsubishi, Samsung, Daikin, or NIBE system can all show the same issues if the underlying design or settings are wrong. The heat pump unit is usually the last place to look.
Common Signs Your Heat Pump Isn’t Working Properly
These are the most common experiences that bring UK homeowners to us for an independent review:
No heating — the system runs but the radiators or underfloor heating produce no useful warmth
No hot water — the cylinder never reaches a usable temperature or runs out quickly
Some rooms remain cold — the system heats well in part of the property but not all of it
Higher electricity bills than expected — the system is running but not efficiently
Constant on-and-off cycling — the system repeatedly starts and stops rather than running steadily
Fault codes appearing regularly — the same codes keep returning even after being reset
Low system pressure — the pressure gauge drops repeatedly and requires topping up
Loud or unusual noises — vibration, banging, persistent gurgling, or excessive humming
Heat pump running all day without reaching the set temperature — continuous operation with no result
Hot water running out — adequate volume one day, barely enough the next
For each of these, there is usually a specific, identifiable cause. And in most cases, it can be resolved without replacing the heat pump or calling out a specialist to site.
Your Heat Pump Runs Constantly
This is probably the single most common concern we hear from UK homeowners:
“My heat pump never seems to switch off is something wrong?”
Sometimes, no. Heat pumps are designed to run for long, steady periods at lower temperatures rather than in short intense bursts like a gas boiler. On a cold day, running for eight to twelve hours continuously is completely normal and is actually more efficient than cycling on and off. That is how the technology is meant to work.
The problem comes when the system runs all day and still cannot maintain the set temperature, or when electricity usage is noticeably higher than expected despite continuous operation. In those cases, continuous running is a symptom of something else:
Poor system balancing heat is not being distributed evenly, leaving some rooms without adequate flow
Low system flow rates restricted circulation preventing heat from reaching the furthest parts of the circuit
The House Never Feels Warm Enough
If the heating runs reliably and yet rooms still feel cold or never reach the temperature you have set, this is one of the most frequently investigated complaints we receive. The heat pump unit is usually working fine the issue lies in the heating circuit that surrounds it.
The four most common causes are:
Incorrect Flow Temperature
Heat pumps deliver heat gradually at lower water temperatures typically between 35°C and 50°C, compared to the 65–80°C a gas boiler produces. If the flow temperature target is set too low for your home’s heat demand, the radiators cannot release enough heat to warm the rooms, even if the system runs all day. This is one of the most commonly misunderstood settings issues we identify, and it is usually correctable without any hardware changes.
Poor Radiator Sizing
Radiators are rated for a specific heat output at boiler-level water temperatures. At heat pump flow temperatures, that same radiator produces roughly 40–50% of its rated output. If your radiators were sized for a gas boiler and never re-assessed for a heat pump, they may simply not have enough surface area to warm the rooms at lower temperatures regardless of how well the heat pump performs.
Closed TRVs
Thermostatic radiator valves reduce flow to a radiator once a room reaches temperature. If too many close at once, total system flow drops below what the heat pump needs triggering flow faults, short cycling, and reduced heating performance across the whole circuit. Using TRVs correctly with a heat pump is fundamentally different from how they were configured under a gas boiler, and settings carried over from a previous installation are often entirely wrong.
System Balancing Issues
In a correctly balanced system, each radiator receives roughly the flow rate it was designed for. When out of balance, radiators near the heat pump get too much flow while those further away receive too little some rooms are comfortable, others stay cold, regardless of how long the heating runs. Heat pump system balancing is rarely completed properly at commissioning and is one of the first things we check when a system is underperforming.
Your Electricity Bills Are Higher Than Expected
Higher-than-expected electricity use is one of the clearest signals that something in the system is not set up correctly and it is also one of the situations where the potential saving from getting the system properly configured is most tangible. We have worked with homeowners where a single settings change reduced electricity consumption by 20 to 30 per cent.
The most common drivers of high running costs are:
Excessive flow temperatures running at 55°C or above when the system should be targeting 40–45°C in most conditions
Weather compensation turned off or set incorrectly the system runs at the same high flow temperature in mild autumn weather as in midwinter
Constant short cycling the system starts and stops repeatedly rather than settling into a steady long run, which reduces efficiency significantly
Incorrect system design undersized emitters or poor pipework forcing higher-than-necessary flow temperatures just to achieve basic heating
Faulty controls a thermostat, zone valve, or controller causing the system to run when it should not
High running costs are almost always a system issue, not an inherent feature of heat pump technology. A well-configured system in a suitable property should cost less to run than a gas boiler not more. If yours feels expensive, the cause is worth finding.
Your Heat Pump Keeps Showing Fault Codes
Fault codes are the heat pump’s way of reporting that something is outside its expected operating parameters. The difficulty is that the code tells you what triggered it not why and the why is almost always more important than the code itself.
Some common examples of what is actually happening behind the code:
Communication faults often point to wiring issues or a damaged controller which may be unrelated to the original fault that preceded them
Temperature faults are frequently symptoms of wider problems incorrect flow temperature settings, inadequate emitters, or an oversized heat pump short cycling rather than running steadily
Resetting a fault code without establishing the cause means the same fault will almost certainly return sometimes within hours. The code is a starting point for diagnosis, not the diagnosis itself.
Your Heat Pump Keeps Losing Pressure
Recurring pressure loss is one of the most common issues we see and also one of the most frequently mismanaged, with many homeowners simply being told to top up the filling loop rather than actually fixing what is causing the drop. Repeatedly adding fresh water introduces oxygen into the closed system, which accelerates corrosion and creates further problems over time.
The most common underlying causes are:
Small water leaks often not visible as a drip; a weeping joint, valve seal, or slow-releasing connection is enough to gradually reduce pressure over days or weeks
Expansion vessel faults the vessel can no longer absorb thermal expansion, leading to pressure that builds rapidly when heating runs then falls again when the system cools
Automatic air vents passing small amounts of water alongside air during normal operation
Pressure relief valve discharging caused by the expansion vessel failing to manage thermal expansion correctly
Recent maintenance a single pressure drop after bleeding radiators is normal and usually just needs one top-up
The key distinction is whether the pressure drop is a one-off or a recurring pattern. If it keeps coming back within days or weeks, there is an underlying cause that should be identified and corrected.
Your Heat Pump Sounds Noisy
Some degree of noise from a heat pump is entirely normal, and many homeowners become concerned about sounds that are simply part of how the system operates. Understanding the difference between normal and abnormal noise saves a lot of unnecessary worry — and unnecessary call-outs.
Normal operational sounds you should expect:
Fan running the outdoor unit fan draws air through the heat exchanger and varies in speed throughout the day
Defrost cycles a rushing or hissing sound as the system briefly reverses to clear ice from the outdoor unit, typically lasting 5–15 minutes
Water circulation occasional flow sounds from pipework, particularly when the system first starts up
Refrigerant movement a quiet hiss or subtle bubbling as refrigerant moves through the indoor unit
Sounds that are worth investigating are those that are new, louder than before, or intermittent in a way you have not experienced previously. Persistent vibration, repeated banging when hot water finishes, gurgling in radiators that does not clear, or unusual electrical humming from the indoor unit can all point to genuine issues:
Air trapped in the system causing irregular heating in specific radiators and sometimes gurgling or knocking at the unit
Restricted flow conditions the system working against back pressure from a blocked filter, strainer, or partially closed valve
Loose mounting vibration transferring from the outdoor unit to a wall, bracket, or pipework
Circulation pump issues a pump that is failing, set to the wrong speed, or creating cavitation noise
Incorrect pipework undersized or unevenly routed runs creating turbulence and flow noise
Often the Problem Is Not the Heat Pump Itself
This is probably the most important thing to understand about heat pump problems in UK homes and the one most frequently overlooked by both homeowners and visiting engineers.
In a significant proportion of the systems we review, the heat pump unit is operating exactly as it should. The refrigerant cycle, the compressor, the temperature readings all within specification. The problems being experienced are caused by what surrounds the heat pump, not by the unit itself. The most common culprits are:
Control settings weather compensation curves, thermostat configuration, and schedule programming that does not suit the property
Cylinder configuration incorrect hot water timing, setpoint temperature, or immersion heater settings
Incorrect system design undersized emitters, wrong pipe routes, or missing components that were specified but never installed
Poor balancing uneven flow distribution that leaves some areas of the house consistently underheated
Blocked filters or dirty strainers reducing flow throughout the circuit and causing knock-on faults
Heating zones working against each other TRV settings or zone valve configurations creating conflicting demands that destabilise the system
This matters because the standard response to a heat pump that is not performing sending an engineer to inspect the unit often returns a “no fault found” result, because the unit itself is fine. The problem is in the system design and settings, and was never examined. Knowing this changes where you start looking.
How Do You Find Out What Is Actually Wrong?
Getting a reliable picture of what is wrong requires looking at the system as a whole not just running through fault codes or checking refrigerant pressure. Heat pumps rely on every connected part working correctly together, and a problem in one area routinely shows up as a symptom somewhere else entirely.
A proper diagnosis looks at all of these together:
The heat pump its operating data, fault history, current settings, and flow and return temperatures
Controls thermostat configuration, weather compensation curve, and schedule settings
Cylinder temperature target, timing, and whether the immersion heater is being used more than it should be
Circulation pumps speed settings and actual flow rate through the circuit
Pipework layout, sizing, insulation condition, and whether any restrictions are present
Radiators and emitters whether they are sized for heat pump flow temperatures, not boiler temperatures
Underfloor heating circuits flow rates, zone balancing, and whether manifold settings are correct
Weather compensation whether the heating curve is active, correctly set, and actually varying with outdoor temperature
When one part of this is incorrectly configured or was never set up properly at installation the symptom almost always shows up somewhere else. That is why a whole-system review consistently finds issues that individual fault-focused call-outs miss.
Need Help Identifying What Is Wrong With Your Heat Pump?
If your heat pump is not performing as expected whether that is a heating problem, a hot water issue, high electricity bills, or recurring fault codes our Fix My Heat Pump service provides independent technical support for homeowners across the UK. We look at the whole system, not just the unit.
We review your photographs, system data, settings, and fault history remotely giving you a specific, clear picture of what is causing the problem and what needs to change. Most heat pump performance issues have a resolution that does not require expensive parts, a manufacturer visit, or replacing the heat pump.
Jun 20, 2026
5 min read
What Pressure Should My Heat Pump Run At?
Read More
Jun 20, 2026
5 min read
What Pressure Should My Heat Pump Run At?
Read More
Jun 17, 2026
5 min read
Why Is My Flow Temperature Higher Than My Neighbour's?
Read More
Jun 17, 2026
5 min read
Why Is My Flow Temperature Higher Than My Neighbour's?
Read More
Recent
Recent
Contact Us
Not Sure If We Can Help?
Not Sure If We Can Help?
Not Sure If We Can Help?
Not Sure If We Can Help?
Not Sure If We Can Help?
If you're unsure whether your heat pump problem can be diagnosed remotely, send us a short description of the issue and we’ll let you know if a technical review is worthwhile. No obligation.
If you're unsure whether your heat pump problem can be diagnosed remotely, send us a short description of the issue and we’ll let you know if a technical review is worthwhile. No obligation.
If you're unsure whether your heat pump problem can be diagnosed remotely, send us a short description of the issue and we’ll let you know if a technical review is worthwhile. No obligation.
