boiler coming on when cold is turned on

goingape · 1 Aug 2011

I have a combi boiler and have noticed that the boiler turns on for a short while when the cold is turned on,works normally when hot is turned on.
Has anyone got any ideas,cheers Christina

compheat · 1 Aug 2011

The best way to stop this happening is to install a mini expansion vessel on the cold feed to boiler.

craig51 · 1 Aug 2011

or you have a dead leg somewhere.

DP · 1 Aug 2011

The best way to stop this happening is to install a mini expansion vessel on the cold feed to boiler.

Perhaps I am wrong (correct me if I am), but is that not what the dead leg is doing i.e. acting as a shock absorber?

gigz · 1 Aug 2011

This sometimes happens if theres a long deadleg on the hot, is it capped off where the tank/cylinder was situated ? And has it just started or from install ?

goingape · 1 Aug 2011

From an install,but no dead legs on the pipework that i can see??Thanks for all replies

adlplumbing · 1 Aug 2011

have you just had new stop tap or water meter fitted

Agile · 1 Aug 2011

I prefer to fit a non return valve on the DHW outlet of the boiler.

Cheaper and usually works to eliminate the problem.

Tony

looneyfitter · 2 Aug 2011

Belive it or not I've never actually came across this although heard about it. What is the actual cause?

bengasman · 2 Aug 2011

This can be caused by a combination of relatively high pressure and plastic pipe ( internal or external ).
Best way to stop this is a non retrun vavle plus shock arrestor on the inlet to the boiler.

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boiler coming on when cold is turned on

compheat

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