Vaillant Combi

[emin-j]

Hi,my vaillant combi stopped producing hot water recently and only leaving the hot tap on full for a considerable time would it work (sometimes).I would have replaced the boiler as it is about 12 - 15 years old but advice from this forum and pals at work persuaded me to repair rather than replace. The general opinion was the diverter valve was at fault so I replaced it (almost £100) I also noticed the domestic heat exchanger leaking so replaced that,another hundred pounds ! and guess what it still doesn't work! Following the troublshooting guide in the manual
it starts by asking 'is the red neon light lit on the boiler switch',no is the answer but that has been gone for years and the boiler has worked fine until now, the book says if its not lit replace the main switch PCB and guess what another £100 ! could it not be just the red neon gone.I have tested for power to the main switch panel, all is ok but what is the process when the hot tap is turned on,does the diverter valve move first then make contact with the microswitches?and then that powers up the pump
which then moves the water to fire up the boiler ?
Any help would be appreciated.The model is VCW GB 240 H

MJ

 

[weargas]

does it fire up when you switch on the tap?

 

[ollski]

Who advised you to throw hundreds of pounds on a 15 year old combi???, for that boiler in general terms the end is not far away.

 

[DP]

The ONLY way forward to successful trouble shooting is by full diagnostics. To have a faulty red indicator is not something that the fault finding guide would take into consideration- it assumes the lights are all OK.

So far the only decent thing you have done is not to discard the boiler.

 

[PEDANTICVINDICTIVEMAN]

Ollskis right, who the hell told you to spend £££s on a 15 year old combi, new cheap ones only last 5 years so even a good qaulity one is at the end of it's life at 15

 

[DP]

I would at 15 years (though this boiler was still in production in '95), still endeavour to have this boiler repaired instead of replaced. To suggest this boiler has reached the end of its life is surely based on lack of familiarity of the build quality and realibility.

If a boiler is to be replaced at 5 year intervals, not forgeting system cleanse and labour costs, existing boiler will be far cheaper to run and maintain. Good quality components and reliable mechanics and electronics make this boiler difficult to repair simply because it does not breakdown like modern day counterparts.

 

[emin-j]

Thanks everyone,a bit of a difference of opinion there then ! I do wish now
i would have gone with my first thoughts and bought a new boiler,every part seems to cost £100 or more and a Ravenheat combi at B&Q is under £400.
Anyway i havent give up yet,in for a penny mmmm.
To answer weargas,no the boiler doesn't fire up and i cant see the pin moving on the diverter valve,i did check the diaphragm in the old diverter valve and couldn't find anything wrong with it other than the needle a bit gummed up so i cleaned it up and put it back in bled the system the missus turned on the hot tap and the needle very slowly moved to make contact with the microswitches and the boiler fired up ! for about 3 seconds then nothing ! Anyway i fitted a new diverter valve because it comes complete with microswitches and i can now rule out that part.I have now taken off the main switch board PCB but at over £100 I'm not keen on replacing that for nothing!After all the boiler did fire up for three seconds previously so i recon it could be ok (hope)What i need to find out is the process of how the boiler fires up,by understanding how the boiler works would give me an idea of locating the problem.By turning on the hot tap this should operate the diverter valve yes? but its not and its a new valve,i have bled the boiler i far as i can tell by following the manual,
is it the diverter valve making contact with the microswitches that take the power to the pump?because if the pump doesn't work the boiler wont fire up will it?I don't mind buying a pump if that is the problem but this trial and error method is getting expensive.
Still,by going on the quotes i had to replace the boiler £1600 - £1900 i'l stick with it for a while yet with a bit of expert help of course.
Thanks again every one but i could do with someone explaining how the system works.
cheers,
MJ

 

[weargas]

when you switch on the hot tap a diaphragm in the water section pushes a pin upwards. looking inside the boiler you should see the arm (with the spring attached) on the back of the servo (bottom centre, with 4 small copper tubes entering it) moving anticlockwise. when it moves it serves 2 purposes.
1. it operates the dhw microswitch.
2. it diverts the pumped water to the diverter valve to move the pin assembly outwards (to the right).
for ch the pin assembly moves inwards.
when the pins free themselves from the microswitches they will tell the boiler to fire. the boiler will fire on low rate for about 5 seconds then come up to full rate.
if the pin on the water section doesn't lift up it could be one of 3 problems.
1. the diaphragm in the water section is stretched/spilt
2. the pin is siezed with limescale (bear in mind there is 2 pins, a loose one which isn't part of the water section and the pin that's connected to the thrust plate.)
3. the venturi located within the left hand side water connection in the water section is scaled/blocked.

 

[emin-j]

Thanks weargas,thats interesting,i did see a black unit (bottom front) with copper pipes atached some i think went to the diverter valve and it had a spring on it,so i need to locate this pin you mention does the dhw microswitch start the pump?if not at which point does the pump start to operate.

thank you

MJ

 

[weargas]

yes, it has to start the pump to move the microswitch.

 

[namsag]

Your valiant is one of the best boilers made and as DP says worth repairing,trouble is you got bad advice from somewhere and changed the expensive divertor which on your boiler very rarely goes wrong.Nine times out of ten no hot water is caused by the the £10 diaphragm in the water section(very bottom of boiler with 4 silver pipes and held in place with central grub screw) being stretched , and on splitting water section to change it the pin and water ways within can be cleaned. occasionally if its been leaking badly the whole valve would need changingTakes about half hour max.