Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and cold.

[armyash]

Hi guys

Went to a job today in a small set of offices and i was told that the hot water kept going on and off (hot then cold). What would you recommend i check? Pressure was low but I topped it up, made no difference.

Is a dodgy thermostat or heat exchanger likely? What tests do i need to do? if not where else should I be looking?

Also before that the women in the office told me that the water flow from the hot and cold taps were poor, checked with a weir gauge and got 3ltr/min.

I was thinking perhaps there is a valve not fully open somewhere. No isolation valves on any of the pipework to kitchen or to the ladies and gents. There was a stopcock on the cold as it comes in to the kitchen from downstairs. This was fully open.

Unfortunately the other offices downstairs were all locked as they are vacant and that is where the mains stopcock is (apparently), i wanted to check that this is fully open or if there are other valves down there.

Any information/advice welcomed.

 

[neily01]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

Prob a blocked hw hex, but knowing vaillant the main hex is prob blocked as well!

 

[armyash]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

Prob a blocked hw hex, but knowing vaillant the main hex is prob blocked as well!

Thanks. Forgot to say that with just hot water switched on the boiler does not fire up. only if it's ch/hw together.

i don't really have much experience with fault finiding. Could be diverter valve??

 

[Millsy 82]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

Whats the cold flow like? A low flow rate like that will prob mean that the phex is getting up to temp quickly and shutting boiler off.

I cant picture the boiler is this the one with all the small bore pipes in it?

Just googled it so know the boiler. You need to find the cause of low flow rate as this prob wont be enough to kick the boiler in.

 

[GrahamM]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

Sounds like divertor valve diaphragm maybe gone.

 

[armyash]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

http://www.vaillant.co.uk/stepone2/data/downloads/73/44/00/combicompactinstallationservicing.pdf

this the MI's for it, i'm just having a look through now.


cold flow is just as poor. The boiler doesn't shut off with CH on just as soon as it's set to HW only it doesn't work.

 

[neily01]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

Its that horrible old thing ! Prob what graham m says, good luck!

 

[stevetheplumber]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

looking at the mi's it needs 3.5 litres a minute minimum flow rateso its possible the flow rate isnt enough to lift the diaphram id ask if the flow has always been that poor before doing anything
you can see the micro switches if you remove the cover if its not moving you can push it down see if it works then i it does i would say change the diaphram first

 

[moogwai]

Re: Valliant only gets Lukewarm very poor water flow on hot and cold.

Any mixer taps installed?? I had one of these where the mixer taps were faulty causing a backflow cancelling out the hw pressure in turn boiler not operating in hw mode......i isolated the mixer taps and hw worked fine.

 

[armyash]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

looking at the mi's it needs 3.5 litres a minute minimum flow rateso its possible the flow rate isnt enough to lift the diaphram id ask if the flow has always been that poor before doing anything
you can see the micro switches if you remove the cover if its not moving you can push it down see if it works then i it does i would say change the diaphram first

Yes I asked if the flow rate has always been that bad and they said no. They said if they renew the lease in a couple of months they will be looking to have a new boiler anyway. I just go to jobs as i'm told so I will check that if i get sent back.

 

[armyash]

Re: Valliant only gets Lukewarm very poor water flow on hot and cold.

Any mixer taps installed?? I had one of these where the mixer taps were faulty causing a backflow cancelling out the hw pressure in turn boiler not operating in hw mode......i isolated the mixer taps and hw worked fine.

Interesting, something I hope I can try. I can cut in a couple of iso's for the mixer and see if that helps.

All good replies if i get sent back to the job i will update.

 

[neily01]

Re: Valliant only gets Lukewarm very poor water flow on hot and cold.

Any mixer taps installed?? I had one of these where the mixer taps were faulty causing a backflow cancelling out the hw pressure in turn boiler not operating in hw mode......i isolated the mixer taps and hw worked fine.

Once went to a job with terrible water hammer throughout the whole house, newly built 5-6 years old.when ever any tap or shower in the house ran it was a right racket! Plumber had been around and told them they would need to dig up all of the kitchen and hall way to replace and lagg pipes correctly as they were bouncin about. Long story short after a bit of investigating tracked it down to a posh kitchen sink mixer that when the taps were run the back pressure would cause the ceramic cartridges to shudder. Confirmed it by simply pushing down on the tap heads to compress the cartridges while using other taps all good! then shutting one iso at a time no probs new taps all sorted! No digging up floors about 2hrs work

 

[jtsplumbing]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

You need to check the incoming water, as you state that both the hot & cold have a poor flow rate , so fault is probably not the boiler

 

[armyash]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

You need to check the incoming water, as you state that both the hot & cold have a poor flow rate , so fault is probably not the boiler

That's the reason i wanted to check all valves were fully open. Thought that would be best before touching the boiler.

 

[RoryD]

Re: Valliant Combi Compact DHW only gets Lukewarm very poor water flow on hot and col

Check ythe servo in the front bottom is making the switch. If not clean the li'l biddy pipes out or order new