vaillant 20/1 T2W CH starts and stops

[Bunnyman]

hi mate we try to help but you seem to have some fantasy about the bloody pd valve....these never fail they react to an external fault as i told you last week.. if the unit works ok on hot water and the pin in the pd valve stays out why would it suddenly go in when you call for heating? the main heatexchanger is no different for heating or water still think prob lies with flow switch does it rise when you put heating on?

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• Bunnyman
• 26 Mar 2010
• 499

 

[gorselands]

Thanks Bunnyman, only replaced the diaphragm 'cos the other was very stretched and the local spares had one. Removed the HE and run hose and compressed air through it seems to be flowing well. Just going on what the second heating guy said was wrong. The flow switch does rise but whetether sufficiently is difficult to see. Everything get very hot when running HW. Maybe need to check the micro switches?? I will plod on trying to eliminate things. But you are probably right and I need a new flow valve. Can order one locally @£160.00. Thanks again, Mike

 

[Bunnyman]

Ok it will run water etc through it as it has built in bypass within the heat exch itself so u will need to fill it with descaler until u can c it comin out the other connection ie kamco HD an leave it 30 min then wash with fresh water don't just run it thro as that won't help if that don't work get aa flow switch

 

[gorselands]

will have to wait 'till next week to get flushing agent but will keep you posted. I do appreciatwe this help. In the meantime have a happy Easter.

 

[gorselands]

Just an update and thank you for your advice. Descaled main heat exchanger using a circulating pump, including bypassing the HW circuit. (As soon as I put a hose through doubted it was the problem). Refitted and CH still not working. Stripped flow switch, dropped wax stat in pan of water and brought up the heat. Worked, but sluggish and had to get water to near boiling. Ordered a new one and hey presto I have CH. So again, many thanks.

 

[Bunnyman]

well done mate i did say it was wax stat at the very beginning,,,u did well to get a wax stat as part obselete since sept last year

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• Bunnyman
• 26 Mar 2010
• 499

 

[gorselands]

Hi Bunnyman, if your still there, and colleagues of course. Boiler working fine, no strange noises and rads nice and hot. However, the flames rise and then lowers about every 7 or 8 secs. Is this what is called modulating and is it a feature of this Vaillant? It didn't seem to do it before. The other boiler doesn't do it. Also temp guage never reads as high as the one for upstairs. I put that down to more rads on and bigger circulation. Any ideas or is all OK? Thanks again.

 

[Bunnyman]

yes its fine its modulating coz the wax stat has now lifted the valve enough to make the lhs micro switch so the variable stat is working...the other ones wax stat is part worn so not lifting valve enough so its working on the fixed potentiometer.. u might as well change the other one before u cant get a wax stat

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• Bunnyman
• 26 Mar 2010
• 499

 

[gorselands]

Well done sir. I forgot to say that I bought the whole flow switch. It would have cost about £50.00 just for the wax stat and up to 5 days delivery. As the other unit came complete and was available locally I decided to spend the extra. I will now order the wax stat and rebuild the one I have replaced as a spare. The temp reads about 42 degs on the downstairs boiler and 62 degs on the one for upstairs. Seems a big difference. The rads are hot enough. Do these temp guages mean much or effect anything else or do they just do what is says on the box - read temps? So as long as rads are hot possible faulty guage not too important? Just out of interest the new flow switch has a narrow tube on the side that the original didn't have. I assume that it is for a later temp probe that on mine is fitted just below the FS. Or am I talking broken biscuits? Cheers.