Vaillant 937 turning on with cold tap?

[gassafe]

A customer today said that his vaillant combi pulses on when the cold tap is turned on?

I said it sounded like a its causing some sort if back pressure & activating the flow switch in the boiler?

What's the best method of curing this? I have never noticed it on any Worcester combi boiler I have ever fitted, its the only vaillant i have ever fitted, is it a vaillant thing?

Is there a way of reducing the sensitivity of the flow switch on a fancy vaillant 937? Or is it a simple check valve before cold feed on boiler, I would have to add mini expansion vessel too then?

 

[Whyme]

look on the boiler sticky thread i posted a fix for it that vaillant told me..you have to reduce the timing before it fires when taps opened.suppose making it less sensitive hope this helps

 

[gassafe]

look on the boiler sticky thread i posted a fix for it that vaillant told me..you have to reduce the timing before it fires when taps opened.suppose making it less sensitive hope this helps

Thanks for that... Can someone post a link to that thread as I can never find anything when searching the forum!!

 

[novicegas]

is it in the diagnostics d 80 - 90, somewhere between those numbers you can have the dhw firing at 1.5l or 3l and 2 secs delay. is that what youre on about?

 

[Whyme]

thats the one. dont know how to post links but its post 4 in boiler breakdown sticky thread, gas safe registered only forum.

 

[gasmanrob]

It's probably when the tap is turned off and the pressure builds up after it dropped when the tap was open. Just enough to move the sensor.

try fitting a mini vessel just at the boiler on the cold inlet

 

[Roger Welton]

Yup, single check valve and mini exp vessel before cold inlet will stop this.

 

[Whyme]

its a known fault on the 937 ( something to do with the store) and just going through the diagnostics sorts it out.

 

[IDCHAPPY]

My ecomax does a similar thing, I've never been bothered it check it out :lol:

 

[IDCHAPPY]

its a known fault on the 937 ( something to do with the store) and just going through the diagnostics sorts it out.

Also be a good deal cheaper than a mini expansion vessel and check valve 😉

 

[Ermintrude]

Well I'm disappointed with this boiler, never had these issues with my old boiler --- oh you mean the broken leaking one with burst elson tank?

 

[lame plumber]

most combis suffer this and prv and shock arrestors seem to be mentioned more and more in mfis nowadays

 

[Ermintrude]

Normally on a poorly installed system or when little to no clips as surge is magnified by oscillations in pipe work. Seen a worn toilet flush flick logic on a few times

 

[armourer]

Stick a non return valve on the cold mains inlet to the boiler. Just use one from a filling loop.

Just had a thought unless its passing through a mixer tap or shower??

 

[gassafe]

I will try the vaillant adjustment first, I don't want to have to fit check valves as they sometimes are noisy! Plus the external expansion vessel, would it have to be a bigger one than normal as the 937 has a 15 litre heat bank, but I guess these have built in vessels for expansion?

 

[Whyme]

I guess these have built in vessels for expansion?

If i remember right thieve got one at the top in the store part.

 

[Ch4 plumbing]

Worcester have changed there mi on combis to include the fitting of a shock arrestor on the incoming cold main if a water meter is fitted due to water hammer and to prevent the above.

 

[albatross]

Probably a dead leg on old pipework somewhere full of air.

 

[IDCHAPPY]

If i remember right thieve got one at the top in the store part.

On the Aquatech there was a 1/2 ltr one right under all the boiler connections

 

[wattsie1987]

Worcester have changed there mi on combis to include the fitting of a shock arrestor on the incoming cold main if a water meter is fitted due to water hammer and to prevent the above.

So have a fair few others. OP d88 is the parameter that needs adjusting.

 

[gassafe]

I emailed vaillant tech, they suggested that there was a dead leg of pipe somewhere... And said to adjust d.88, if that does not cure then a check valve or shock arrester... So thanks everyone, we all seem to be signing from the same hymn sheet for a change 😛