Boiler firing when the cold water is turned on

[Gabriela]

Hi all,

Hope you’re all doing well.

I had a new bathroom installed recently which involved new piping, and also capping off some redundant pipes. Since then, my boiler (pretty new Vaillant combi) turns on when I turn the cold water on. I’ve done some reading and it seems like the problem is air trapped in the pipes. I don’t think I can release the air as I suspect it’s trapped in the ‘dead-leg’ pipes which have been cut off and capped - these are now inside my bathroom wall, starting aprox 1 meter high and probably going up in the loft and then coming down again somewhere else?? (I used to have a traditional boiler and the water tank was in the loft).
The recommended advice online is to have a non-return valve and a mini shock-absorber installed to the cold feed on the boiler. Is that difficult, expensive? Will it look bulky?
Is there any other way to fix the issue? If I can identify the pipe where the air is trapped, could I make a small hole inside it to release the air and then cover the hole somehow?

Also, the pipes cut by the plumber used to feed my old shower, which I’ve moved. Should the plumber have left the capped pipes inside the wall or should he have cut them from the loft, so that they are always accessible? What’s the common practice?
Can I remove them not somehow? Perhaps cut them and cap them in the loft?

Here they are in the photo.

Many thanks

 

[Deleted member 120897]

I think you’ve answered a lot of your own questions in relation to the boiler firing - yes, it’s due to capped dead leg pipework, any good plumber would have insisted they be removed. Pipes shouldn’t be left capped anywhere unless temporary or no greater than twice the pipe size diameter.

 

[ShaunCorbs]

Bad to leave compression cap ends in a non accessible wall

 

[Ben-gee]

Yes you should be able to cut them off in loft, remove as much of the unused pipe as possible.
I always remove completely- not because I’m a strict follower of best practice, more that I’m tight and it all goes in the scrap box!!