Can you solve my Vaillant combi boiler problem, Sherlock?

  • Thread starter Grimly Feendish
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Grimly
Well have you turned off the valves on the central heating flow and run the hot water?
Have you tried restricting the water flow at the tape (if not on the cold water inlet pipe)
After fitting the sardine tin exchanger the thruput of water is greater to some extent


This boiler is built like excrament house doors used to be in my youth. Generally nothing much goes wrong with them except new rubbers - which you should certainly replace every 10 years - or so. If you do get someone to repair, then get them to see to all the rubbers.
 
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Grimly Feendish

Thanks Bogstandard

Ive just measured the water flow. It is 13.6 litres per minute (should be 9-11 apparently). If I turn down the cold water intake below that the boiler does not fire. So my problem appears to be: -

1. Too fast throughput of water through the dhw system, and consequently luke warm water.

2. Any strangling of that throughput stops the burners igniting. Of course if I strangle it whilst the boiler is burning (whether at the tap or at the cold water feed cock) its stays lit and the water eventually heats up. If I turn the tap off with the restricted flow at the cock then no ignition at all.

Does that point to anything?

Grimly
 
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Scrufflepeck said:
What exactly is a crock of horse poo? I thought I was giving pretty solid advice - and some work for a hard pressed heating engineer, which is surely what we should all be trying to do isn't it? I mean, I dont know about you, but I need the work and if a boiler is marginal and I haven't a clue how to mend the piece of junk, and the customer wants the nice shiny new one that Ive told him about at a price he can afford, I'll be more than happy to take his money. Come on lads, we'd all be bankrupt if we didn't pad a little - its standard industry practice!

if you dont know how to mend a piece of junk, which just so happens to be one of the best combination boilers ever produced, perhaps you shouldnt be selling your services to the general public. Perhaps that is why you are so quiet and need the work? You keep on padding. Id rather sleep sound at night with a clear concience.
 
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Grimly Feendish

Just tried turning off the CH valves and running hot water. No difference. The nub of the problem is that the boiler will not fire unless the water flow is maximum, and at 13.6 litres per minute it is too fast to heat the water.

Any ideas?

Thanks all.

Grimly
 
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Grimly Feendish said:
Ive just measured the water flow. It is 13.6 litres per minute (should be 9-11 apparently). If I turn down the cold water intake below that the boiler does not fire. So my problem appears to be: -

1. Too fast throughput of water through the dhw system, and consequently luke warm water.

2. Any strangling of that throughput stops the burners igniting. Of course if I strangle it whilst the boiler is burning (whether at the tap or at the cold water feed cock) its stays lit and the water eventually heats up. If I turn the tap off with the restricted flow at the cock then no ignition at all.

That would point to two problems! The flow rate is too high and needs to be reduced on the valve underneath AND the diverter valve diaphragm is failed.

We would normally replace the whole unit as we have to give a full guarantee to our clients.

Your previous plumber was quite correct to advise replacement of the plastic HE as they were totally unsatisfactory and leaked badly.

Tony
 

Rob

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Grimly Feendish said:
Ive just measured the water flow. It is 13.6 litres per minute (should be 9-11 apparently). If I turn down the cold water intake below that the boiler does not fire.

Then it sounds like you need a new water section, if you look at the boiler directly in the centre is a servo valve when a hot tap is run the water valve underneath this operates and moves the servo valve over, If this really isnt happening at anything less than 13ltr a min then then water section (£80) needs replacing.
 
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Grimly Feendish

Thanks lads! I think we got there! Just one point of clarification if I may. Are the water section (per Robo) and the flow valve and diverter valve (per Tony) the same thing?

Cheers

Grimly
 
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Grimly Feendish

Actually Im now really confused! Ive located the water section (directly below the servo valve) and Ive located the diverter valve which is over to the right and slightly above. Please could Rob and Tony attempt to reconcile their advice and point me in the most probable direction?

Tony, are you suggesting that the entire diverter valve needs replacing? What about the water section?

Rob, you advise replacing the water section, but is the diverter valve implicated (or could it be) in any way?

Thanks v much.

Grimly
 

Rob

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Like i said you need to check the servo valve cam moves across and makes the microswitch. Usually @ around 4 ltrs a min.

If however it hardly moves or takes 13lt a min for it to operate then this is where your fault lies and the water section, which houses a diaphragm, needs replacing.
 
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Grimly Feendish

Rob, the servo valve only operates (ie moves about half a cm to the left and then the boiler fires) at full flow rate ie 13.6 litres. So that is conclusive? What about Tony's suggestion of the diverter valve? I cant find water sections for sale online for this model.

Cheers

Grimly
 

Rob

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Tony probably knows these boiler 10 times better than me so only he can answer. However the water section does need replacing.

Here is the part, more expensive than i thought.

http://www.partscenter.co.uk/parts/index.html

The second photo is shows it with a temp adjustment.

Rob

edit link not working. but type 'water valve vcw'
 
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Water valve diaphragm kit, is less than a tenner.
I don't see how it's anything to do with the diverter valve.
 

DP

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This post is amazing. How can someone set out to repair a boiler without any idea whatsoever, of how it works.

IF YOU KNOW the water at hot tap is TOO HIGH and reducing it does not fire the boiler, what does that tell you. DIAPHRAGM IS KNACKED.

Grimly Feendish, if you are a registered gas installer, get competent and learn your trade. Blindfolded diagnostics will get you no where and gives others a bad name.
 
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Grimly Feendish

DP said: -

"Grimly Feendish, if you are a registered gas installer, get competent and learn your trade. Blindfolded diagnostics will get you no where and gives others a bad name."

DP I know nothing about gas installation and I do not have the faintest clue what you are talking about or what prompted that intervention. I am a mere mortal who is using this forum for what I assume is its intended purpose, namely for lay people like me to get a little help or a few pointers from people with experience. As it happens it seems I have achieved just that, with the problem being narrowed down to the water section diaphragm.

Thanks to all for your help.

Grimly
 

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