Radiators don't stay hot long

[thesmoothound]

Hi.i had a new central heating system installed around 3 years ago with a combi boiler. have been happy with it.however, I have always noticed that the rads never seem to hold their heat for long after the boiler is off.i just thought it was a combi boiler thing.they get really hot but are cold within 20mins. It was only until my mate has had his boiler replaced with a combi and his rads stay warm for much longer after the boiler is off. Should I turn down the return valve?

Any suggestions would be great.

Thanks

 

[Doggit]

The rads getting cold quickly, is a result of thin metal in the rads themselves. Heat quickly, and then get cold quickly.

 

[Agile]

Well, not actually thin metal.

But the low water content of the rads.

So little heat in the small volume of water.

They will also heat up quicker.

Makes for a much more efficient system.

Tony

 

[thesmoothound]

Thank you for your answers. Very helpful.

 

[motorbiking]

It could also be a lack of insulation in the pipework, allowing the system to cool quicker. But making sure each rad is bled will help maximise the amount of water in them.

 

[Agile]

Once the heating is off, the pump will be off and so no circulation.

Therefore pipe losses will not affect the cooldown time of the rads.

 

[motorbiking]

Sure, but the water in the rads would arrive colder and therefore cool quicker. Typical combi's work on a 20 °C differential between flow and return? With insulated pipes (particularly if in cold spaces) you could find a drop of 10 °C between boiler and rad depending on heated temp. If its cold in 20 mins then it would take longer to get cold.

PS - I didn't do the calcs, but I could

 

[bernardgreen]

Once the heating is off, the pump will be off and so no circulation.

Pump overrun springs to mind, most boilers seem to have a period of over run, and it seems to vary from boiler to boiler.

 

[Aquaheat]

Pump overrun springs to mind, most boilers seem to have a period of over run, and it seems to vary from boiler to boiler.

An average of about 3 mins is going to make very little difference. Pump overrun is purely to stop water sitting in what could be a very warm slab of metal. It moves this residual heat into the system anyway.

 

[mcmoby69]

Your mate might have had his set up incorrectly and the guy who did yours set it up right!

If your heating goes off at 9am because you leave for work at 9:10am why are you bothered that it cools down so quick?

 

[motorbiking]

The job of the radiator is to.. er radiate. so the quicker it extracts heat from the water in to the room the better job its doing.