Why Are My Heat Pump Radiators Only Lukewarm? Common Causes Explained

Many homeowners contact us because their heat pump appears to be running normally, yet the radiators never feel particularly hot. Unlike traditional gas boilers, heat pumps operate at lower temperatures, so radiators may feel warm rather than hot to the touch.

However, if the house struggles to reach temperature or rooms feel cold, there may be an underlying system issue worth investigating.

1. Heat pumps run at lower temperatures

A gas boiler might run at 70–80°C, while heat pumps typically operate around 35–50°C.

This means radiators often feel lukewarm compared to gas systems, even when the system is working correctly.

2. Poor system circulation

If the system has poor flow through the radiators, heat will not transfer effectively.

Common causes include:

• Incorrect pump settings

• Sludge or debris in pipework

• Long pipe runs restricting circulation

• Incorrect buffer tank connections

3. Radiators undersized for heat pump temperatures

Heat pumps rely on larger radiators or underfloor heating.

If the original radiators from a gas boiler system were kept, they may not emit enough heat at lower temperatures.

4. Incorrect system setup

In some cases the issue is simply configuration:

• Flow temperatures set too low

• Weather compensation incorrectly adjusted

• Controls cycling incorrectly

• Zone valves restricting flow

5. When to seek a technical review

If your heat pump runs for long periods but the house still struggles to warm up, a professional review may help identify whether the issue relates to system design, flow rates, radiator sizing, or control settings.