Radiators · Naples and Campania
Heat pump not heating: causes and what to check
A heat pump that is not heating is often not broken: it is protecting itself from a water circulation problem, it is defrosting, or it is running on wrong settings. The display and parameters say a lot, which is why a video call works well here.
Quote before we start about 1 hourBleeding, valves, leaks, balancing
Do not open the outdoor unit or the heat pump's electrical panel: parts stay live even when the machine is stopped. If the cylinder has an electric element or runs high-temperature heating cycles, water can come out very hot, so beware of scalding.
Recognise the problem
- The radiators or the floor stay lukewarm
- The shower water comes out barely warm
- The display shows a flow or high pressure error
- The outdoor unit stops, gives off steam, then restarts
- It is fine during the day, but the house is cold early in the morning
- It locks out and restarts only after a reset
The most common causes
- 1
Not enough water circulating
Clogged water filter, air in the system, low pressure or closed valves. The flow switch, the sensor that checks that water is flowing, notices and stops the machine with an error.
- 2
High pressure in the circuit
In heating mode, the high pressure error often appears when heat cannot pass into the water: too many thermostatic valves closed, low flow, or a flow temperature, the water leaving towards the system, that is too high.
- 3
Settings and weather-compensation curve
With a curve that is too low, the machine sends lukewarm water just when it is coldest outside. Time slots, eco mode or a thermostat in the wrong spot can also make a healthy system look faulty.
- 4
Domestic hot water: cylinder and three-way valve
Shower water is heated in a cylinder. If the three-way valve, which sends the hot water either to the cylinder or to the system, is stuck, or the cylinder probe reads wrongly, the shower stays lukewarm.
- 5
Defrost or refrigerant gas
On cold, damp days the outdoor unit stops now and then to melt ice: this is normal. If instead its output is steadily poor and frost forms in odd places, gas may be missing because of a leak.
What you can safely check yourself
- Photograph the error code and note when it appears: by day, at night, while you shower.
- Check the system pressure gauge: if the pressure is below the value given by the installer, it is an important clue.
- Check that the thermostatic valves are not all closed and that the valves under the machine are open.
- See that the outdoor unit is clear of leaves, sheets or objects and has space around it.
- If you see steam from the outdoor unit with the fan stopped for a few minutes, wait: it is defrosting.
Never open the boiler or the gas water heater, and always switch off the power before touching an electrical appliance. If in doubt, call us.
When you need a technician at home
- Flow or high pressure error that returns after the reset
- Water filter to remove and clean with the system under pressure
- Three-way valve or probes to replace
- Suspected refrigerant gas leak
- System pressure that keeps dropping
Error codes: brand and model are needed
Each manufacturer uses its own codes. A code like E006 has no meaning valid for every brand: it must be read in your model's manual, otherwise tables found online risk leading you astray.
Before the video call, photograph the label on the outdoor unit and on the indoor one, if there is one, and keep the manual or the app to hand. With this data the code can be interpreted in a few minutes.
Many flow switch and high pressure lock-outs come from the same place: the water is not circulating as it should. Before replacing parts it is worth checking filters, pressure and valves.
Radiators, floor and hot water: what to expect
The heat pump performs best when it sends water that is not too hot. With underfloor heating it is in its element; with cast-iron radiators designed for an old boiler it can struggle on the coldest days.
So a radiator that feels less hot to the touch than in the boiler days is not necessarily a fault. What matters is that the room reaches the temperature you want, even if it takes longer.
If shower water is lukewarm always at the same time, the cylinder's time slots or a temperature set too low are often the reason. These adjustments are easy to see on the display.
Want to know what it is first? Show us
You show us the display or the app with the error code, the system pressure gauge, the outdoor unit and the water filters. Together we read the parameters, weather-compensation curve and time slots, and we guide you through safe checks. If the machine needs opening or the refrigerant gas needs work, we tell you what kind of work is required.
Video consultation, up to 15 minutes: €9.90 (€14.90 on Sundays), deducted from the bill if we then come to your home.
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Frequently asked questions
Why is my heat pump not heating the hot water?
The most common causes are a cylinder temperature set low, wrong time slots, a faulty probe or a stuck three-way valve. On a video call we look at settings and codes, and if a part needs replacing we tell you.
What does a flow switch error on a heat pump mean?
That the machine does not sense enough water passing and stops to protect itself. It often comes from a dirty filter, air in the system, low pressure or closed valves. If the error stays after these checks, the flow switch itself may be faulty.
Is the high pressure error dangerous?
It is a protection: the machine stops before causing damage. In heating mode it usually means heat cannot pass into the water. Do not keep resetting it; it is better to understand why it happens.
Smoke is coming from the outdoor unit: is it a fault?
Almost always it is defrost steam, normal on cold, damp days: the unit stops for a few minutes and then restarts. If instead you smell burning or see dark smoke, cut the power and call a technician.
The radiators are less hot than before: is the heat pump faulty?
Not necessarily. It works with cooler water than the old boiler, so the radiators feel lukewarm to the touch. What matters is whether the house reaches the set temperature.
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