A customer of mine with a heat pump asked a good question recently: his cylinder display showed 50°C, but his bath only measured about 43°C. Where was the heat going?
It's a common question, and there's usually nothing wrong.
Got a Megaflo or unvented cylinder problem in Orpington, Bromley or south east London?
I'm a G3-qualified engineer and service and repair all makes of unvented cylinder. Cylinder service £140, no VAT to add.
1. A bath is never as hot as the tap
When I measure hot water at a service, I run the tap fully on hot for about a minute and hold the thermometer in the running water. Measured that way, his taps were giving 50°C. Once water is in the bath, it's lost heat to the cold bath itself, the air, and the time it took to fill. Losing 5 to 7°C is completely normal.
2. The water in the pipes goes cold overnight
The first hot water of the day has been sitting in the pipes for hours. Run the hot tap for a minute before filling the bath.
3. The lever isn't fully on hot
With single-lever mixer taps, being even slightly off full hot mixes in cold water.
4. The tank temperature goes up and down
Heat pumps heat the cylinder to its set temperature, then let it drop a few degrees before heating again. Depending on when you run a bath, the tank might be nearer 45°C than 50°C.
5. A blending valve may be fitted
Some systems have a thermostatic blending valve, either on the cylinder or at the bath, which deliberately limits the temperature at the tap for safety. On new baths, this is often required.
How to get hotter water
- Time it: set the hot water to heat an hour or so before your usual bath or shower time, or use the hot water boost on the controller about 30 minutes before.
- Turn it up a little: raising the cylinder temperature from 50°C to 52–55°C makes a noticeable difference. It costs a little more to run with a heat pump, but not much.
- Get the settings checked: clocks, schedules and heat pump settings all affect it. I check them at every service.
If your taps are well below the cylinder temperature even when measured properly in the running water, it's worth having it looked at. Heat pump servicing is £190 and cylinder servicing £140, or £285 for both, with no VAT to add.
Need it looked at?
If your cylinder is losing pressure, dripping at the tundish, making noises or not giving you hot water, I can come and find out why. Annual cylinder service £140, or £285 with your heat pump. No VAT to add.
Cylinder getting on a bit? If it's 15 years or older and giving you trouble, a replacement often makes more sense than repeated repairs. Unvented cylinders supplied and fitted from £1,550.