Vaillant Boiler VCW GB 242EH

[gadget_buster]

I have a problem with my boiler, it will give hot water on demand but will not fire up for central heating. There is a signal coming from the room stat as the pump runs and the fan comes on. Someone told me it could be the thermistor but i am unable to locate it. Does anyone know where they are? I was told a way to check them (when found) was to put a resistance test across them it 200k and i should get a resistance of 14-25 ohms. Any help would be greatly appreciated.

 

[kevplumb]

check the servo valve is returning properley after drawing water

 

[chrishutt]

Very unlikely to be anything to do with the NTC probe (thermistor). These boilers have a complicated operating mechanism that few people understand (but kev makes a good point above). You need to find someone who does. It could be Vaillant, but I expect they're expensive. I suggest ringing Vaillant and asking if they have details of local engineers who've done their course for the VCW Combi compact.

 

[gadget_buster]

does anyone know where the thermistor is so i can check it?

 

[kevplumb]

inside the combustion chamber CORGI job

check the servo valve first

 

[gadget_buster]

Sorry to be a right pain in the arse, but could you run through the sequence of operation for hot water and CH for the diverter/servo valve, would it be the same for both. When i run the hot water tap the probe from the valve comes out and releases one of the two microswitches, (the other microswitch was not being depressed), when the tap is turned off the probe returns back in and one of the microswitches is depressed. It is exactly the same process when the heating is demanding heat from the room stat. The thermistor looks like it is ok ( (thats not the problem) it had a resistance of 15.7ohms

 

[andsam]

As the previous posts have suggested the NTC thermister on the Vaillant is one of the most reliable componants you will come across.

It would be more like the servovalve that is sticking.

I have already replied to your questions with the same answers you are now recieving from this forum.

Andy.

 

[DP]

Why would you want to check the thermistor? Boiler has not fired for central heating. Thermistor comes to play sometime after the burner is alight.

I am surprised you have not taken the hint that Kev and others are giving you.

 

[Agile]

I have never seen a working temperature sensor on a boiler which had a restance of 15.7 ohms.

Are you sure you know how to measure resistance?

I have more confidence in the reliability of vaillant parts than your measurements!

Tony

 

[gadget_buster]

A supposed competent corgi registered vaillant expert said that the resistance should be that, i am only acting on advice i have been given, that is why i went down that route of questioning, after all i was told it could be one of twenty things. I feel a little trodden upon here, i have explained what the servo valve is doing and no one comments on that, just about how much of a fool i am for not taking the previous advice. The previous advice has been taken and i am responding best i can. I thought this was meant to be a helpful site, not one where everyone puts me down (it is enough for one person to say to me follow the previous advice), i get the hint and i will look again at the servo valve. i did ask if the sequence of its rise and fall of the valve was correct but no one has responded to that, i do thank Andy for his simplified advice and his lasting patiences, but was wondering if my valve is doing as it should with both demand for hot water and CH?

 

[chrishutt]

I thought this was meant to be a helpful site, not one where everyone puts me down

Did everyone put you down? You might want to rephrase that.

With regard to the servo valve and it's operating sequence, you're asking a lot for a detailed explanation. As I said, it's a complicated control system, involving hydraulics, pneumatics and mechanics as well as electronics, so you'd have a do your homework first. Have you studied the manual, for example?

 

[ChrisR]

Diverter on the right should go out for HW and in for CH. Controlled by the servovalve.
Your resistance figure is probably a thousand times out

 

[gadget_buster]

Many thanks for your help
So would you say there is a problem with my diverter valve then if it goes out for both CH and DHW?
If i was to strip the valve and check the control lines are not blocked do you think that would help?

 

[kevplumb]

Diverter on the right should go out for HW and in for CH. Controlled by the servovalve. [/b]

what is the servo valve doing

 

[gadget_buster]

if the servo vavle is the little triangular device in the middle front of the boiler that has three copper control lines going to it and the device turns a cam that makes contact with a microswitch behind it, then it is only operating when the DHW is demanded, when the CH is demanded the sevro does not operate and the spindle on the diverter comes out like ti does when the DHW is demanded. Hope this helps?
Thanks for your help