Combi boiler activated when cold tap turned off??!!

[armyash]

Hi guys

Went to a job late last night. HW working fine. CH working fine.

Strange thing is when a cold tap is turned on or the toilet is flushed, a couple of seconds later the boiler starts up the HW light flicks on for a split second and then it goes off again. It doesn't actually fire up but something is making it think it should.

Boiler is a Potterton Combi Heatmax type.

Just out of interest I Isolated the cold inlet and cracked the nut and the water was coming out warm (after the isolation valve).

The cold and hot pipes from the boiler are touching where they run towards the kitchen sink. (don't think that is an issue other than looking rubbish).

Another thing, the customer is having a new shower room installed upstairs, the pipework has been run for first fix and the shower guts are all connected up. Could this be causing the issue?

Any questions ask away, i'm stumped. Was thinking perhaps there's a some sort of faulty flow switch or something is piped up wrong but really I have no clue and hoping someone here has come across something similar.

Thanks

 

[Scott_D]

Air trapped in the pipe or a shock arrest needed

 

[rpm]

Was this a emergency Dyno call out? lol

 

[armyash]

Air trapped in the pipe or a shock arrest needed

Could it be air trapped from where recent plumbing has been done?

I don't know what a shock arrest is so will have to look that up. Customer was 70 years old and said she can't pin point when the fault started but said it became increasingly more noticeable since the plumbing work started.

 

[Masood]

Are there NRVs on the shower?

 

[armyash]

Are there NRVs on the shower?

Not that I could see unless they are built inside but no seperate nrv's on the pipework.

That was my initial thought as soon as she said a new shower was being fitted.

 

[Masood]

Not that I could see unless they are built inside but no seperate nrv's on the pipework.

That was my initial thought as soon as she said a new shower was being fitted.

I'd start with that mate...

 

[Destroyer2813]

As said already possible air in a dead leg somewhere where the waters been drained to work on pipework

 

[Simon F]

is there ant old hot water pipe work that has just been capped when changed to a combi?
vent pipe in loft?
this will alow the pressure in the hot side to drop when cold is used, then when the tap is shut there is a slight flow back down the hot side.

 

[armyash]

is there ant old hot water pipe work that has just been capped when changed to a combi?
vent pipe in loft?
this will alow the pressure in the hot side to drop when cold is used, then when the tap is shut there is a slight flow back down the hot side.

It was converted to a combi 2 years ago. I think it's all becoming clearer.

I haven't checked the loft yet.

If I have to go back I'll know what to look for.

I wasn't aware of this fault before so it's good to know.