Vaillant Sine 18 Fault. No Central Heating.

[londondave]

Hi all,

Any advice on this problem Id really appreciate.

Friends Vaillant Sine stopped working. He had 2 plumbers round saying the boiler needed to be replaced for wrong reasons (ignitor not working no parts availalbility) etc.

Ignitor worked fine, but i found the overheat switch open circuit, so i pushed the black knob in and it started to work agaiin for DHW.

When the central heating button gets clicked though the boiler fires up for about 15 seconds, initially full rate, then half rate, then it cuts out.

I checked the signals to the pump and they run when ch is on.

Hot water seems to be being circulated around the inner boiler but not to the central heating circuit.

If I remove the nTc purple wire it fires up fine, but still doesnt circulate to the ch circuit.
It seems to me as if the water in the NTC zone gets too hot and the boiler switches off on CH, because there is no way of getting the water circulated out of the boiler and therefore it overheats. This problem doesnt occur when running dhw hotwater from the tap and it appears to cool down the heat exchanger. I dont think the NTC sensor is faulty as it only cuts the gas out when its pipe is really hot.

I tried flushing water through the rads to make sure not blocked and okay. Also i reverse flushed water from the return circuit round the rads and backwards up into the boiler and out the pressure overflow to see if flow can go that way and to dislodge any debris and it flushed backwards fine.

I am suspecting the ch valve in the divertor (behind the dhw heat exchanger) is either jammed for DHW and not letting ch water flow. Or there is some reason a sensor or something is signalling to it to remain locked in the DHW position and not CH.


Please can anyone pour light on to this one ?

Also can anyone advise where instructions or for this boiler or associated diagrams.?

Many thanks

Dave

 

[tipintim]

Well confusing.. Whats the problem with thhe system

 

[tipintim]

what is ntc, excuse my ignorance

 

[londondave]

what is ntc, excuse my ignorance

NTC sensor is the one on the pipe coming down from the burner to the divertor valve. when it gets too hot the boiler is supposed to cut the heat at the burner. If theres a fault on the NTC sensor, or if the water in the pipe is too hot then sometimes removing the NTC sensor cable allows the boiler to refire up (used for diagnositc purpose only!)

 

[oldplumber]

check diverter valve is operatiing ok either jammed or diaphragm split. ttim, go buy yourself a copy of john reginalds books off amazon and all will come clear one for ch and one for combis

 

[londondave]

Also if anyone knows the likely part numbers needed again, i'd be very grateful.

CHeers

Dave

 

[londondave]

check diverter valve is operatiing ok either jammed or diaphragm split. ttim, go buy yourself a copy of john reginalds books off amazon and all will come clear one for ch and one for combis

Thnaks oldplumber. How do you check if the divertor valve is working ? Under the torch last night i didnt see the way to manually move it .

 

[tipintim]

NTC sensor is the one on the pipe coming down from the burner to the divertor valve. when it gets too hot the boiler is supposed to cut the heat at the burner. If theres a fault on the NTC sensor, or if the water in the pipe is too hot then sometimes removing the NTC sensor cable allows the boiler to refire up (used for diagnositc purpose only!)

High limit stat = ntc ????

 

[oldplumber]

I'm afraid to say if you dont know that you shouldnt be touching a boiler so call in a registered technician, unless of course someone else wants to advize you, and Im not happy to encourage tampering by the uninitiated.

 

[londondave]

High limit stat = ntc ????

Thanks, but not on this boiler. THeres a separate temperature limit stat on this boiler. The NTC is on the pipe location i described (pipe between burner and divertor valve), the high limit stat is a probe right at the top lhs of the boiler, which connects to a resettable switch by the control board/ pcb section at the bottom.

 

[tipintim]

was that directed at me??

thats directed at u oldplumber

 

[londondave]

I'm afraid to say if you dont know that you shouldnt be touching a boiler so call in a registered technician, unless of course someone else wants to advize you, and Im not happy to encourage tampering by the uninitiated.

you ask a simple question, like 'how do you move this divertor valve manually' and you get a patronising response like this ? Ive followed a logical line of dignosis here, where the other gas registered engineers have tried to rip off the customer announcing this boiler cant be fixed, and this presumpitous book reccomnder says call in another 'registered technician' !

For anyone out there that can offer help, yes I'm on the gsr.

 

[AllyBongo]

Diverter could be faulty or clogged up, is the flow getting any heat at all?

 

[oldplumber]

my advice was for the op and to whom it applies, as things dont add up as far as I can see here, as we are talking about basic knowledge of boilers and combis ie whats an ntc or how to check a diverter valve, which anyone who has done time with a rgi would have learnt on the job. Maybe Im wrong but thats only my opinion and now the moderaters will be jumping on me for upsetting people but so be it coz what I'm reading should be common knowledge for anyone working on gas appliances..

 

[tipintim]

you have to tell me what ntc stands for. is it a speciall boiler

 

[tipintim]

my advice was for the op and to whom it applies, as things dont add up as far as I can see here, as we are talking about basic knowledge of boilers and combis ie whats an ntc or how to check a diverter valve, which anyone who has done time with a rgi would have learnt on the job. Maybe Im wrong but thats only my opinion and now the moderaters will be jumping on me for upsetting people but so be it coz what I'm reading should be common knowledge for anyone working on gas appliances..

Never ment to upset you. Sorry for what ever i did wronge. Andy

 

[londondave]

I'm afraid to say if you dont know that you shouldnt be touching a boiler so call in a registered technician, unless of course someone else wants to advize you, and Im not happy to encourage tampering by the uninitiated.

You ask a simple question like how do you manually move the divertor valve on this boiler, having followed a pretty logical line of diagnosis, and this presumptions book recommendor comes out with a recommendation to go and get a 'registered techncian in'. Thanks for that the last two 'registered technicians' tried to rip off the customer and tell him the necessary parts cant be sourced. For anyone out there that can advise, yes I am on the gsr.

 

[londondave]

Diverter could be faulty or clogged up, is the flow getting any heat at all?

cheers, no the flow pipe is getting no heat at all. I think this probably is the diverter.

Some one told me you can get overhaul kits for them, any one know if yuo can get straight replacements ?

 

[tipintim]

what is your gas safe number bud

 

[AllyBongo]

dunno much about that model, but if your divertor is stuck, when the ch is on the water will go through the dhw x changer and overheat. You should be able to feel the pipework for heat

 

[AllyBongo]

NTC relates to the thermistor, like PTC. Negative or positive temp co-efficient

 

[Puddle]

the wax cartridge will be broken in the diverter valve
The normal position for the diverter to sit is in the hot water mode position

When heating is called for the water heats in the boiler and there is a wax capsule in the bottom of the diverter valve that expands and pushes the diverter valve open for hot water to flow around the heating side,

 

[tipintim]

Still waiting to find out what NTC stands for
Can you lighten me

 

[londondave]

dunno much about that model, but if your divertor is stuck, when the ch is on the water will go through the dhw x changer and overheat. You should be able to feel the pipework for heat

Cheers, yeah thats pretty much exactly whats going on. pipe between burner to divertor is hot. divertor itself is hot. pipes to heat exchanger hot, one of the pipes from the divertor to the return side pump is hot, but the flow pipe coming out of the boiler is cold. I'm 90 % its the divertore valve, not moving but partly wondering if other factors (like a weak pump) could be something to do with it.

I am also concerned its not getting the right signals/ inputs e.g. the wax stat to move on the diverter. So dont know if the diverter is jammed, or if its not getting the right inputs to move.

Not to sure I want to swap the divertor to find it could be e.g. the wax stat or other....

 

[londondave]

not too sure, its a thermistor (resistance thermometer), but not too sure what it stands for exactly