Why is my house still cold with a heat pump

Why Is My House Still Cold With a Heat Pump?

A heat pump that runs all day but leaves your home feeling cold is one of the most frustrating problems a homeowner can face. You've made a significant investment, the system is clearly doing something but the rooms never quite get there.

The good news is that there is always a reason for it. In most cases the heat pump itself is not the problem. What's usually happening is that something in the system design, setup or controls is preventing the heat from reaching the rooms properly.

This guide walks through the six most common causes, what each one looks and feels like in practice, and what needs to happen to fix it.

1. The flow temperature isn't matched to your home

Flow temperature is one of the most important settings on a heat pump system, and one of the most commonly set incorrectly. It's the temperature at which water leaves the heat pump and circulates through the radiators and if it's wrong, the whole system underperforms.

Set it too low and your radiators won't emit enough heat to warm the rooms, even with the system running for hours. Set it too high and you're wasting electricity without any real benefit to comfort.

What this looks and feels like:

• Radiators are warm to touch but never hot

• The system runs almost continuously through the day

• The house hovers a degree or two below where you want it, particularly in cold weather

• It feels like the heating is always "nearly there" but never quite arrives

Weather compensation is meant to solve this it adjusts flow temperature automatically based on outdoor temperature. But we frequently see systems where the weather compensation curve is set too conservatively, or where flow temperatures have been capped by an installer trying to improve efficiency at the expense of comfort. The result is a house that stays cold.

2. Radiators haven't been sized for a heat pump

This is the single most common cause of a heat pump not heating a house properly, and it's a design issue that starts before the system is even installed.

Gas boilers run at high flow temperatures typically 65–80°C. Radiators were designed and sized for that. Heat pumps run at much lower temperatures, usually between 35–50°C, which means the mean water temperature inside a radiator is significantly lower. And a radiator's heat output is directly proportional to the difference between the water temperature and the room temperature.

At a mean water temperature of 42°C in a 20°C room, a standard radiator gives off roughly 40–45% of its rated output. Not half less than half. If nobody accounted for this when designing the system, the radiators simply cannot emit enough heat to keep the house warm.

This shows up most in:

• North-facing rooms that always feel cold regardless of how long the heating runs

• Older properties where the original radiators were never replaced

• Systems where the installer did a "like-for-like" swap from a boiler to a heat pump without reviewing the emitter circuit

3. Heat is being produced but not reaching the rooms

Sometimes the heat pump is working exactly as it should, but something in the distribution side of the system is preventing that heat from getting into the rooms. This is more common than people realise and can be surprisingly difficult to spot without a proper technical review.

Causes include incorrect pump settings, partially blocked strainers or filters, air trapped in the system, and flow rates that are too high or too low for the pipework layout. When any of these are present, the heat pump runs continuously, electricity usage climbs, but the rooms stay cold which leads most people to conclude the heat pump isn't powerful enough. Often it is powerful enough; it just can't deliver what it's producing.

4. The controls are fighting the system

Heat pumps are fundamentally different from gas boilers in how they should be controlled, but the majority of systems we review are still set up with boiler logic. This creates a quiet, persistent conflict between how the system wants to operate and how it's being told to operate.

A heat pump performs best when it runs steadily for long periods, modulating its output based on outdoor temperature through weather compensation. It doesn't suit being switched on and off by a standard room thermostat, and it doesn't suit having its run times heavily restricted by timers.

Common control problems that leave houses cold:

• Thermostats set to switch the system off when the room reaches temperature, then back on when it drops creating a constant on/off cycle that prevents the system from ever reaching equilibrium

• Timers that limit run time to a few hours in the morning and evening, which is enough for a boiler but not for a heat pump

• Weather compensation either not enabled or configured with a curve that's too shallow for the property

5. The property's heat loss is higher than the design assumed

Every heat pump installation should begin with a heat loss calculation a room-by-room assessment of how much heat the property loses in cold weather, which then determines the size of heat pump and radiators needed. If that calculation was inaccurate, or if it was skipped entirely, the system may simply not be capable of keeping up with the actual heat demand of the house.

Properties where this tends to be an issue include older solid-wall homes where insulation levels were assumed rather than verified, houses with significant draught problems, properties where recent extensions or loft conversions were not factored into the original design, and any home where the heat loss calculation was done using software defaults rather than actual measured data.

The clue is that the system can just about cope in mild weather but noticeably struggles once outdoor temperatures drop below around 5°C.

6. The original system design has fundamental errors

This is the conversation nobody wants to have, but it's a real cause of cold houses and an under diagnosed one. If the system was poorly designed from the start, no amount of adjustment to settings or controls will fully fix the problem.

Design errors we see regularly:

• Heat pump sized too small for the actual heat demand

• Flow temperatures specified incorrectly for the property's emitter circuit

• Poor pipework layout creating circulation problems

• Unnecessary buffer tanks adding thermal mass that slows the system's response

• Low loss headers installed where they weren't needed, diluting flow temperature

A system with design errors might still function it just won't perform properly, and the occupants end up living in a house that's never quite warm enough.

What a properly working heat pump should actually feel like

Part of the reason this problem persists is that many homeowners aren't sure what "normal" looks and feels like with a heat pump. It's worth being clear about this.

A heat pump won't produce the same intense blasts of heat you get from a gas boiler on a high flow temperature. Radiators will feel warm rather than hot. The system will run for longer periods sometimes continuously in cold weather rather than cycling on and off. None of that is wrong.

What should be consistent is the result: your home reaches and maintains a comfortable temperature. If it doesn't if there are rooms that never warm up, or the whole house sits a couple of degrees below where you want it that isn't how the system is supposed to work, and it needs to be looked at.

What to do if your heat pump isn't heating your home properly

The first step is getting a clear picture of what's actually happening. Most cold house problems with heat pumps are the result of multiple smaller issues working together a flow temperature that's slightly off, radiators that are slightly undersized, controls that aren't quite right. None of them is catastrophic on its own, but together they add up to a house that never quite gets warm.

A proper technical review looks at the system as a whole: the design, the flow temperatures, the controls setup, how heat is being distributed through the property, and whether the original specification was appropriate for the home. From that, you get a clear picture of what's causing the problem and what the practical steps are to fix it.

If you're dealing with this, our Full Performance Review covers exactly this system design, flow temperatures, controls and heat delivery and gives you a written report with clear, practical recommendations.

View full details and pricing here →