boiler coming on when cold is turned on

[goingape]

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]

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

 

[craig51]

or you have a dead leg somewhere.

 

[DP]

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]

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]

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

 

[adlplumbing]

have you just had new stop tap or water meter fitted

 

[Agile]

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]

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

 

[bengasman]

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.