Boiler firing when cold taps turned off

[tommy8884]

We recently had our heating and water system replaced with a combi. One thing that's really frustrating and probably costing us money, the boiler fires every time a cold tap, toilet or appliance is closed. This also seems to cause a build up of pressure in the hot taps. We have fairly high flow rate and there is a bit of pipe hammer when you shut off the taps. In order to try and resolve I put a hammer arrestor under the kitchen sink (not where the stop cock is). This seems to have stopped it at that tap, but the others still do it. Short of spending 200 quid on arrestors for every appliance and outlet, what are my choices? I read an NRV on the cold feed into the boiler might help?

Note I have tried as much as possible to remove all air from the system but I suspect we have some dead legs buried in walls and floors from all the work that will have air in. Also I did get the plumber back and his solution was to reduce the tap flow by turning the shut offs a bit. He then legged it (and it hasn't worked, but has reduced it a bit)

 

[cross thread]

Pressure reducing valve and a mini expansion vessel should sort it,dead legs are best removed

 

[gas112]

there is a dead leg on a hot water pipe is the old hot supply capped in airing cupboard . Although you hear the boiler kick in it usually isnt on long enough to fire up

 

[tommy8884]

there is a dead leg on a hot water pipe is the old hot supply capped in airing cupboard . Although you hear the boiler kick in it usually isnt on long enough to fire up

Yeah there is a capped pipe in the airing cupboard. I know there are two capped in the kitchen wall as well, hot and cold. Can't get to those. I could have the airing cupboard one ripped out when we have the bathroom done.

 

[gas112]

Yeah there is a capped pipe in the airing cupboard. I know there are two capped in the kitchen wall as well, hot and cold. Can't get to those. I could vale the airing cupboard one ripped out when we have the bathroom done.

if the airing cupboard one is capped with a compression cap you could loosen it a bit and let any trapped air out and tighten it back up

 

[tommy8884]

if the airing cupboard one is capped with a compression cap you could loosen it a bit and let any trapped air out and tighten it back up

You might just have cracked it for me. Not a lot came out (maybe 2 seconds), but it seems to have stopped the issue as far as I can tell. Will monitor it. It quite tricky to tell as the worst tap is the furtherst from to boiler so it's tricky to hear it.