Regular To Combi Boiler Cold Tap Woes...

[Keef1234]

Hi everyone, I'm a new member and hope someone can offer advice re a new Combi install a few months ago...
The issue I have is that the new WB4000 starts up when any cold taps are turned off (or the cistern is flushed).
More info:

1) This combi boiler has replaced an ancient Apollo (regular boiler) sited in the kitchen where the old boiler was.
2) The installer also fitted a new radiator in a 3rd bedroom extension (where there wasn't one originally - just the HW cylinder/pump etc).
3) He hasn't removed pipework or tanks in the loft due to the very tight area - has a bad back !!
4) The work started back in Aug 2023, but after 5 weeks of irregular visits we still only had hot water - no CH...
...installer claimed it must be a faulty boiler...
5) WB engineer called and found the new radiator inline valve in off position - once turned on the CH sprang to life
(his report included fitting a shock arrestor)
6) Original installer came back yet again and installed shock arrestor to no avail - scratched his head and left...
...he did mention that there is a (new ??) 'cold water feed upstairs' - which didn't make sense to me...
...I don't think he removed cold water feed to unused dishwasher as requested or repair a small leak near stopcock...
(capped it off myself)

Looking thru the posts on here it transpires we might need one or two (??) NRVs fitted, or it could be a 'deadleg'...
The hot water cylinder was taken away - the 2 large pipes leading to it have been capped off both ends...
(but one of them at least seems to still be under water pressure !!??)

We have 2 original mixer taps - one in kitchen seems to have 2 separate spouts...
...the one for bathroom shower (unpowered) seems to only have one.
Dunno if that might present a problem.

I am loath to get the original installer round again, as despite being a very friendly guy, I don't trust his competence.
As a DIYer I'd be happy to follow any advice offered before hiring a prof plumber - cheers

 

[terryplumb]

Dead leg would be my first suspicion. Fit check valve on the DHW pipe immediately after the boiler.

 

[Keef1234]

Many thanks for the superfast reply, tho I'm a bit confused as to the difference between a CV and a NRV...
Apparently they are slightly different, or will either do the same job ??
(the pipe is vertical if that makes any difference...)

 

[terryplumb]

Essentially they are the same thing ,only allow water to flow in one direction . A double check valve has two non return valves inside it ,for double protection.

 

[Keef1234]

Thanks again - am picking up a 15mm pipe cutter and double CV tomorrow
Two quickies if u don't mind...

1) Will a double check valve slow hot water flow to the DHW taps ??
2) When fitting the CV (before cutting the DHW outlet pipe), do I turn off stopcock, drain all taps, turn off boiler then proceed...
...or is only some or all of that necessary ?? (can't find the answer to that anywhere !!).

 

[terryplumb]

No ,flow to hot taps shouldn't make any appreciable difference.
Close mains water stopcock. Isolate electric supply to boiler. Turn on hot and cold taps to drain water.

 

[Keef1234]

Just fitted the Double CV - as it turned out, quite an easy job...
PLEASED TO REPORT IT IS NOW WORKING FINE WITH NO PROBS !!!
Thankyou very much for your expert advice...
Tho as it has now proved to a dead leg, do I need to employ a plumber to trace where it is to avoid danger of legionnaires disease ??
(and would the dead leg be in a hot or a cold pipe ??)

 

[terryplumb]

You need a better plumber !
Dead legs really need to be eradicated ,only onsite investigation will determine where they are, very likely on the hot pipework.

 

[Keef1234]

You need a better plumber !

But where to find 'a better plumber' is the problem
Tis a shame that the more helpful, experienced, knowledgable guys on here can't advertise...
...even my local plumbing shop ('Plumbwiser' who charge £75 per hour) had never heard of the issue I had with the combi boiler !!

Seems 'check-a trade' is not rated on here... 'check-a-conman' is how they are described - fairly or not (tho I suspect it is 'paid advertising').
I guess that the maze of pipework and tanks in the loft needn't be there any more, so I'll try and find someone willing to take them away...
(leaving only necessary pipes in situ)

Thanks again