Heat Pump Not Working? Here's What to Check Before Calling an Engineer

A heat pump that suddenly stops heating your home or producing hot water feels alarming, but it doesn't automatically mean the unit has failed. In our experience diagnosing heat pump faults remotely across the UK, a large proportion of "breakdowns" turn out to be simple issues with power, controls, or settings not the heat pump itself.

Before you pick up the phone and book an expensive callout, there are several safe, straightforward checks any homeowner can carry out. Working through them in order can often tell you exactly what's wrong, and in many cases can get your system running again the same day.

Why Heat Pumps Stop Working: The Real Picture

Heat pumps are more complex than a standard boiler, which means there are more potential points of failure but it also means more of those points can be checked without any technical training. The most common causes we see are:

• A tripped or isolated power supply

• A fault code the system is displaying but nobody has noticed

• Low system pressure on a sealed heating circuit

• Thermostat, schedule, or "away mode" settings preventing the system from calling for heat

• A problem isolated to hot water only, or to a single heating zone

Working through the checks below in order will usually point you toward one of these causes.

1. Check the Power Supply First

Before anything else, confirm that both the outdoor heat pump unit and the indoor controller are switched on and receiving power.

• If the controller screen is completely blank, this points to a power supply issue rather than a fault with the heat pump itself. Check the isolator switch and fuse spur near the unit.

• If a circuit breaker or RCBO trips and you reset it, and it trips again, stop resetting it. A breaker that trips repeatedly is protecting you from an electrical fault, and repeatedly resetting it can be dangerous. This needs to be investigated by a qualified engineer or electrician.

2. Look for a Fault Code Before You Touch Anything

Most modern heat pump controllers display a fault or error code when something has gone wrong, even if the symptom you've noticed is simply "no heating."

Take a photograph of the fault code before resetting the system. This single step makes a huge difference to how quickly a problem can be diagnosed whether that's by us, your installer, or the manufacturer's technical support line. Resetting the unit first often clears the code and the fault becomes far harder to trace.

3. Check the System Pressure

If your heat pump runs a sealed heating system (the majority of UK installations do), check the pressure gauge on the controller or on the system itself.

• Low pressure can cause some heat pumps to stop operating entirely, or to display a pressure or flow-related fault code.

• If you top up the pressure and it keeps dropping again over hours or days, that points to an underlying leak somewhere in the system. This needs investigating rather than repeatedly topping up.

4. Check Your Thermostat and Controls

It sounds obvious, but a surprising number of "heat pump not working" calls come down to the system simply not being asked to produce heat. Check:

• The thermostat is set above the current room temperature

• Your heating schedule is set correctly for the time of day

• The system hasn't been left in holiday, away, or eco mode

• Wireless thermostat batteries aren't flat

It's also worth establishing whether the problem affects your whole house or only one heating zone. A single-zone fault points toward a valve, actuator, or zone thermostat issue rather than a problem with the heat pump unit itself — we recently diagnosed exactly this on a system that kept turning on and off due to an over-zoned design, if you want to see what that can look like in practice.

Heating Works But No Hot Water? Or the Reverse?

These two symptoms tell you very different things.

Heating works, but no hot water: the heat pump itself is very likely fine. The issue is more likely to sit with the hot water controls, the cylinder temperature sensor, the motorised diverter valve, or a settings problem in the controller.

Hot water works, but no heating: this points toward the room thermostats, zone valves, circulating pumps, or heating-specific controls rather than the heat pump's core operation.

Separating these two symptoms early on saves a lot of wasted diagnostic time, whether you're troubleshooting yourself or briefing an engineer. One of our recent cases involved a homeowner with no heating or hot water at all, convinced the heat pump had failed the unit turned out to be working perfectly, and the real cause was a leak hidden inside a wall that had nothing to do with the heat pump itself. It's a good example of why working through symptoms carefully matters more than assuming the worst.

Should You Reset Your Heat Pump?

A single reset can sometimes clear a temporary fault and get the system running again. However:

1. Always photograph any fault code first.

2. If the same fault returns after a reset, don't keep resetting the unit. Repeated resets without addressing the underlying cause can mask a developing fault and, in some cases, make it harder to diagnose later.

What Not to Do

Checking your controller, thermostat, and system pressure is safe and something every homeowner can do. Attempting to go further is not.

Don't remove any covers, and don't attempt electrical, refrigerant, or internal repairs yourself. These require specific tools, F-Gas certification, and manufacturer knowledge, and should always be left to a suitably qualified heat pump engineer.

Do You Actually Need an Engineer to Visit?

Not always and this is where many homeowners spend money unnecessarily.

A large number of heat pump problems can be diagnosed remotely simply by working through the controller settings, fault codes, system pressure, and how the heating and hot water are behaving. In many cases, the underlying cause can even be identified and resolved during a single initial call.

Where a site visit genuinely is required, having a clear remote diagnosis beforehand means the engineer arrives already knowing what to investigate — which saves time, and usually money, on-site. This matters more than people expect: we've seen cases where three separate companies had already declined the job before the actual cause was identified, simply because nobody had worked through the diagnosis properly first.

How We Diagnose Heat Pump Faults Remotely

If you've worked through the checks above and your heat pump still isn't working properly, this is exactly the kind of problem our Fix My Heat Pump service is built for.

We work through your fault codes, controller settings, system pressure, and how your heating and hot water are behaving, to identify exactly what's wrong independently, and without any commercial interest in selling you a repair or a new installation. Where it's safe to do so, we'll guide you through simple checks with the aim of getting your system working again during that first consultation. If an engineer is genuinely needed, we'll tell you exactly what to ask them to investigate, and can support them directly by phone or video call if required.

If your heat pump has never performed well since it was installed, or you suspect the original design or sizing may be the underlying issue rather than a new fault, our Pre-Installation Design & Heat Loss Review is worth reading about too it's designed to catch exactly these kinds of design and sizing problems, either before installation or as part of understanding why an existing system underperforms.

Heat Pump Not Working?

If you've been through these checks and you're still not sure what's wrong, we'll help you identify the problem and give you a clear plan for getting your heat pump working again.

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