Vaillant VCW 242E, 282E, DHW temperature problem.

[misanthropicgit]

Our Vaillant VCW242 has suddenly developed a problem where it cannot heat up the hot water sufficiently. It normally produces hot water (I don't know the temperature but it's too hot to touch probably 60-65C) at about 9 litres/min. This morning I had to reduce the flow at the tap to 3 litres/min to get hot water at the same temperature, so running a bath takes ages and the shower is useless.

The boiler is probably well over 15 years old (we've been in the house 9 years) and I've replaced a lot of the 'water' side components: diverter valve, diaphragm, heat exchanger, extraction fan etc. and I'd noticed that the boiler would fire up with a lowish flame and then flare up (i.e. gas flow increase) after 5 seconds or so. Now it all fires up ok but it doesn't seem to have the increase in gas flow, so the burners are not supplying as much heat per unit time as they were yesterday (about 1/3 in fact). I am guessing that there is a mechanism that checks something (perhaps water flow or pressure) before telling the regulator to increase the gas flow to maximum.

Assuming my guess is correct, then the fault would be in the sensor, the control circuitry or the gas regulator. The probability of an electronic failure with no other symptoms is low. If the fault is on the gas side it is beyond my ability to safely repair but it would be useful to have other input.

Does anybody have any ideas or has anyone seen these symptoms before?

 

[Agile]

The sensor would have to go low resistance but at least that is something that you could check cold with a meter.

But its more likely to be a gas related problem. Low pressure from meter, blocked pipes or blocked gas valve etc. Just possibly an electronic fault but thats much less likely.

If the sensor tests OK, and they rarely fail on your model, then you need a competent CORGI, ideally on a no-fix no-fee as this is not a run of the mill fault and will need someone who is at least half competent!

Tell us what it turns out to be!

Tony

 

[misanthropicgit]

Tony

Thanks for response. I agree with you that a gas pressure problem is most likely.

I would like to check the sensor (temperature presumably). I am an electronics engineer so I should be able to do so; however I could do with some guidance on the location of the sensor, and info on what I'm looking for would speed things up. What sort of resistance range should I expect? (not got a lot of experience with thermistors specifically), and a rough guide of resistance change per degree (or similar) would be useful. Is there a datasheet/manual out there somewhere that could help?

 

[DP]

OP, send me a PM for possible answer to your problems. Doubt it is the gas valve that is at fault.