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thermostatHeat Pump Fault Finding

Heat Pump Not Heating Properly? Here’s Why

If your air source heat pump is not getting the house warm, it is usually the way it was set up rather than the unit itself. Fault finding and optimisation across Orpington, Bromley, Sevenoaks and Kent.

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buildSettings Checked First
descriptionWritten Findings

paymentsDiagnosis Visit

  • check_circle£170 full service & diagnosis, no VAT
  • check_circleFlow temperature & curve reviewed
  • check_circleRadiator output assessed honestly
  • check_circleSystem flow rate & pressure checked
  • check_circleWritten report with the findings
buildThe Real Causes

Why It Is Not Getting Warm Enough

I get called to a lot of heat pumps that owners have been told are "too small". Genuine undersizing does happen — but in most cases the equipment is capable and something in the setup is stopping it doing its job.

Weather compensation curve set badly

The most common cause of "it is fine in autumn but hopeless in January". The curve should raise flow temperature as it gets colder outside. Set too shallow, the system simply never delivers enough heat on the coldest days.

Radiators never resized

When a gas boiler comes out, the emitters usually stay. Radiators sized for 70°C water cannot deliver the same output at 45°C. Sometimes the honest answer is that one or two radiators need upsizing — and I will say so rather than pretending settings alone will fix it.

Being run like a gas boiler

Deep overnight setbacks and switching off during the day. A heat pump recovers slowly by design, so a house that has been allowed to drop five degrees will not catch up quickly. Running steadily at a lower output usually gives a warmer house for less money.

Poor flow rate

A blocked strainer, sludged system or an undersized pump starves the heat pump of flow. The unit protects itself by cutting output, and the symptom is a house that never quite gets there.

Cylinder priority stealing heat

On systems with a hot water cylinder, an over-frequent or over-long cylinder priority cycle means the heating is off for long periods. Set sensibly it is unnoticeable; set badly it takes the edge off the whole house.

Genuine undersizing

It does happen, particularly on grant-era installations where the heat loss calculation was optimistic. But it should be the last conclusion after everything above has been checked, not the first.

helpFAQ

Heat Pump Heating Questions

Most often flow temperature and weather compensation set wrong, radiators that were never resized when the gas boiler came out, or the system being run like a boiler with deep setbacks. Genuine capacity problems exist but are much rarer than people assume.
No, and this catches a lot of people out. A heat pump runs much lower flow temperatures, so radiators feel warm rather than hot. The house still reaches temperature — it just does it steadily rather than in bursts.
Sometimes, but far less often than blamed. Before anyone tells you the unit is undersized, the flow temperature, weather compensation curve, radiator sizing and system flow rate should all have been checked. I check those first.
Output drops as outside temperature falls, which is normal and designed for. If the weather compensation curve is set badly, the system fails to raise flow temperature when it should — so it feels fine in October and inadequate in January.
Usually. In most cases it is settings, and settings cost nothing to change. If it genuinely needs a couple of radiators upsizing I will tell you that honestly rather than pretending a tweak will solve it.
Sometimes, but far less often than it gets blamed. Flow temperature, the compensation curve, radiator output and system flow rate should all be checked before anyone concludes the unit is undersized.
Occasionally yes, and I will tell you honestly if so. Often it is one or two rooms rather than the whole house, which is a much smaller job than people fear.
That is treating the symptom at the most expensive possible price. Direct electric heating costs roughly three times what the heat pump costs to deliver the same warmth. Fix the cause first.
Then I diagnose it and quote the repair at a fixed price. But I check settings first, because that is where the answer usually is.

Get Your Heat Pump Working Properly

£170 with no VAT, written findings, across Orpington, Bromley, Sevenoaks and Kent.

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Before You Call

Worth Checking Yourself First

A few of these you can rule out in five minutes without any tools.

Are the radiators warm rather than hot?

That is normal for a heat pump and catches nearly everyone out. Lower flow temperature means radiators feel warm, not scalding. The house should still reach temperature — just steadily.

Are you running deep setbacks?

Turning it right down overnight or when out, boiler-style, is one of the most common causes of a house that never feels warm. Heat pumps recover slowly by design. Try a smaller setback for a few days.

Is one room cold, or the whole house?

One cold room is usually a balancing or radiator sizing issue in that room. The whole house being cool points at flow temperature, the compensation curve, or system flow rate.

Has it got worse as winter came on?

Fine in October, poor in January is the classic signature of a weather compensation curve set too shallow — the system simply never raises flow temperature enough when it genuinely needs to.

Any error or fault codes showing?

Note them down before you call. Codes point straight at a system area and save diagnostic time, which saves you money.

photo_cameraDiagnosis

Looking Properly, Not Guessing

Settings first, then the mechanical side.

Air source heat pump fan and coil inspected during diagnosis
Fan blade and condenser coil exposed for inspection during fault finding
How weather compensation changes flow temperature With weather compensation, flow temperature rises only as the outside temperature falls. Without it, the system runs at a fixed high flow temperature all winter. Outside temperature — colder to the right Flow temperature Fixed high flow compensation off Weather compensated mild day: lower flow, better efficiency cold day: flow raised only when needed Illustrative only — the correct curve depends on your property and emitters
Weather compensation raises flow temperature only as it gets colder outside, rather than running at a fixed high temperature all winter. The curve shown is illustrative; the right setting depends on your property.
Text description of this diagram

The chart plots flow temperature against outside temperature, with colder conditions to the right. A red dashed horizontal line shows a system with weather compensation switched off: it runs at a fixed high flow temperature regardless of the weather, which wastes electricity on milder days. A green sloping line shows a weather compensated system: on a mild day it runs at a lower flow temperature, which is more efficient, and it raises the flow temperature only as the outside temperature falls. The curve shown is illustrative only; the correct settings depend on your property, its heat loss and the size of your radiators or underfloor system.

callCall Gary — 07717 846247