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Central Heating

2 circuits or trapped air?

Hello, I have a large house running 23 cast iron radiators from a buderus boiler with a pump installed on the flow..... some radiators throughout the property are piping hot but some are flat cold. The cold ones are cold even behind the TRV's - so neither flow or return pipes are so much as warm. The system has been bled and balanced - but there seems to be no method rhyme or reason to which radiators are cold - e.g ones red hot, then the next rooms cold and the room after that is hot. Is it possible that there is a valve somewhere in the house that would open up a second circuit or is it possible that there's a secondary valve on the cold rads that's closed. I opened a screw type valve with a large allan key head at the bottom of a cold radiator (directly under the trv) to be met with a face full of cold water (the pressure forced the valve out quicker than I expected) did get slightly warmer as I was screwing back in though.

2 Answers from MyBuilder Heating Engineers

Seems like the pump is not man enough


Answered 26th Dec 2015

I agree with the other contractor. The pump sounds like it is too small for your house. Cast iron radiators hold a lot more water than steel radiators and the pipe work is often larger too. So the pump has to be capable of shifting a larger volume of water.

Unless the system has been drained recently then I wouldn't expect an air lock. If you have drained down recently. Switch off the boiler and open the bleed valve and let the water run from the bleed valve for at least a few minutes per radiator. Hopefully, the bleeded water will be come warm and the system should work again.


Answered 10th Mar 2018

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