Recently, we took a call from an elderly resident who was understandably worried.
She’d had an air source heat pump installed…
She still had hot water…
But her heating hadn’t worked for three days.
When something like that happens in winter, it’s stressful. The immediate thought is: “The system has broken.”
But in this case, it hadn’t.
What Had Happened?
When the installer attended the property, they discovered that the hot water temperature had been adjusted to 66°C.
That might not sound like a big change – after all, many people are used to traditional boilers delivering very hot water.
But here’s the key difference: Most air source heat pumps can’t efficiently produce water at that temperature.
Why Is My Air Source Heat Pump Not Heating My Radiators?
Unlike a traditional boiler, most air source heat pumps can only do one job at a time:
- Heat your radiators
or - Heat your hot water cylinder
Not both simultaneously.
And in most systems, hot water is prioritised.
So what happened was:
- The hot water target was set to 66°C
- The heat pump tried to reach that temperature
- It couldn’t get there under normal operation
- It stayed in hot water mode
- The heating never switched back on
From the resident’s point of view, the heating had “stopped working”.
But in reality, the system was stuck trying to satisfy a temperature it couldn’t realistically reach.
What Temperature Should Hot Water Be Set To?
Most heat pump systems are designed to heat hot water efficiently to around:
50–55°C
Many systems also run a weekly high-temperature cycle (for legionella protection), which temporarily increases the temperature automatically.
But manually setting the cylinder permanently to the mid-60s can cause problems like this.
Will This Increase Electricity Bills?
Hot water mode is when a heat pump works hardest. Producing higher temperatures reduces efficiency.
In this case, the issue was fixed quickly, so the installer wouldn’t expect a dramatic bill increase — but yes, it would have used more electricity than normal during those few days.
The Important Takeaway
If you have an air source heat pump and:
- You still have hot water
- But your heating has stopped
- And there are no obvious faults
It may be worth checking your hot water temperature setting before assuming something has broken.
Heat pumps work differently from boilers. They are designed to run steadily and efficiently or “low and slow”.
If You’re Unsure, Ask
Heating systems can feel complicated – especially when they behave differently from what you’re used to.
If you’re a Lancashire resident and something doesn’t seem right with your air source heat pump, we’re here to help you understand what might be happening before you worry.
Greener Homes in Lancashire offers free, impartial advice — no pressure and no sales. Call us directly on 0800 058 4066 or book a call back here: Free Advice
Sometimes it’s not a fault.
It’s just a setting.