R u sure u changed the heat exchanger on the lhs of the boiler? You have classic symptoms?
Vaillant Combi Boiler - HW Issue
- Thread starter speshman
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Yup, bottom left. Looks like an oversized sardine tin with 4 pipes off it, one from the heat exchanger up top to the diverter valve and then one from cold water to dhw outlet. Was a bit of a pain in the butt to change tbh, wouldnt want to do it again as i've bugger all space to the left of the boiler in the cupboard :s
Its the second change its had too, the original plastic one died a miserable leaky death!
Its the second change its had too, the original plastic one died a miserable leaky death!
Mmm well if u have to put the stat knob on 8 to get ch to fire u have a weird fault, if ur a sparky just check the muppet who changed ur original ht exch didn't cut the link on the pcb, it says to do it in the fitting instructions but is completely unnecessary , it's on the middle pcb facing upwards and is brown , if it has bin cut then twist the wires back together
Might be a red herring with that, hopefully its unrelated. I'm trying hard not to spend money on it as come the end of Jan the boiler will be binned anyway as the house is going to be redeveloped into flats - just need to keep it going 
I'll check that link tommorow - tbh i'd read that elsewhere but wasnt sure where it was located.
I may also pull the heat exchanger and see if it is bunged up out of curiosity, see what I'm feeling like tommorow as its a bloody mission
I'll check that link tommorow - tbh i'd read that elsewhere but wasnt sure where it was located.
I may also pull the heat exchanger and see if it is bunged up out of curiosity, see what I'm feeling like tommorow as its a bloody mission
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Sounds very much like a slow running pump to me. If you are a sparks change the pump capacitor. It's inside the pump terminal box. You should be able to source one from Maplins or RS components. If no improvement change pump.
For gods sake agile
Hmm, pump has a 5 micro farad on it that looks original and tests ok. Popped a rad off and ran the heating to see what the flow is like and it's pretty substantial, especially considering microbore. I keep being steered to the overheat thermistor in the combustion chamber though... If its disconnected all is well and the other overheat on dhw seems to function ok with some applied extra heat to the pipe adjacent. Now I've not taken the front internal cover off yet for fear of gas etc but peeking through the window it seems that there is nothing gas like I can disturb by taking the cover off. Is that correct?
Also is that thermistor that I have in my head as faulty replaceable and if so where to get one from? I'll probably change it anyway just to satisfy a hunch if nothing else.
Also is that thermistor that I have in my head as faulty replaceable and if so where to get one from? I'll probably change it anyway just to satisfy a hunch if nothing else.
We dont advise that DIYers open the combustion chamber.
The NTCs are dry pocket and better in my experience if they are refitted with some heat transfer paste.
They should read about 1300 Ω at room temperature.
Tony
The NTCs are dry pocket and better in my experience if they are refitted with some heat transfer paste.
They should read about 1300 Ω at room temperature.
Tony
The ntc very rarely fail on these and if the overheat on the vcw main ht exch trips it has to be manually reset so u can forget that. The over heat stat on the hotwater pipe cuts out if tap temp goes above 65c so it's not that. If ur sure the dhw ht exch is new u have a circulation prob as 831 said blockage or slow pump
by taking off the combustion cover you are disturbing something gas like!!!!it's the ""combustion cover""""", not advisable to take off, cos it's illegal for you to do so. also i tend to agree with the pump cos there is a lot more resistance in pumping round the boiler via plate hex than through the system. had a similar fault on an ecomax this week, fitted new pump head, all was well, even though heating was working
One problem is that no-one knows what the last engineer did. It does like the burner pressure hasn't ever been checked or adjusted as the seal is still fitted and these do have a tendency to creep up over time.
It will need checking by an rgi that knows the vcw's
It is very possible that the pump has lost it's mojo as mentioned many times already. You can get an indication of this by removing the three screws holding the pd valve in place (the black triangular item in the top centre attached to the gas valve ( it is safe to do so)) and push the pin in with the pump running. If it can be pushed in, the pump will most likely need changing.
If the green light dims, the NTC is working.
If you have a temperature differential meter, I can run you through some checks to verify a blockage or scale in yur circuit.
It will need checking by an rgi that knows the vcw's
It is very possible that the pump has lost it's mojo as mentioned many times already. You can get an indication of this by removing the three screws holding the pd valve in place (the black triangular item in the top centre attached to the gas valve ( it is safe to do so)) and push the pin in with the pump running. If it can be pushed in, the pump will most likely need changing.
If the green light dims, the NTC is working.
If you have a temperature differential meter, I can run you through some checks to verify a blockage or scale in yur circuit.
good luck with that then lol! they will sell u boiler that won't be req
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