vaillant combi boiler

[ctj666]

Help !!!

I am having problems with my Vaillant TURBOmax VUW 282E combi , for 1 week now since we returned from holiday we have had no heating & no hot water.The heating was left on whilst we were away , but appears to have locked out sometime during the week. The boiler will not light , just keeps locking out.I have changed the main switchboard and the main gas solenoid.It goes through it's sequence , the pressure differential switch is working , it sparks , but does not light.There is gas before the gas valve but not after it. Anybody any ideas , your suggestions would be greatly appreciated. Thanks

[Andy]

There is a problem on these, after umpteen years, a flowswitch which is visible down the bottom in the middle somewhere ( if you take the front panel off ), gets to respond veerrryyy slowly, and might eventually just quit I supppose. Most noticeable with hot water, as a delay in the CH coming on is not really noticeable.

I don't imagine it's your problem as you do't seem to have had previous problems with it, but just to rule it out, have someone turn a hot tap on, and watch the flowswitch ( which has a pipe coming out either side, and a lever coming out of a diaphragm on top, which drives a red microswitch ), to see if it moves. Specifically, the lever coming out of the top. If not, actuate the red microswitch by it yourslf ( carefully, use an electrician's insulated screwdriver to avoid accidents ), and see if that kicks it into life.

Andy.

[Ed Sirett]

Whilst it's true that this unit uses a water flow driven diverter valve which is a stock fault for this and similar boilers this is not likely to be the problem here.

I'm assuming the OP knows that the ignition gas rate on these boilers is likely to be around 2mb and then after ignition the gas rate will move up to around 10mb (IIRC). The 2mb might be hard to spot on the gauge as the levels will hardly have cleared the centre section of the gauge.

Anyway I'll assume that the OP has eliminated this problem. The gas valve is mains operated (99% sure) and then the higher rate is called up on the modulator using low voltage wires.

I would check to see that the 230V is getting to the gas valve, if it is then there is a gas valve problem if it isn't then it a PCB problem.

Since the OP has changed the gas valve perhaps the problem was the PCB all along?

[jms019]

My few year old Vaillant's gas valve has just stopped too.

It did the same trick a couple of years ago, took weeks and over xmas for my plumber to find a replacement in Scotland (I live in Cambridge) and cost me =A3200 or so. I wrote to Vaillant in the new year and they said there was no parts problem.

Funny thing is if I plug the connector into the old supposed broken valve now it clonks open when it should.

I fear there is a serious design fault (like it only just works under some conditions) somewhere concerning the electrical properties of the solenoid, the diode(s) or something.

Jon

[jms019]

I think I know why it has been running for ten minutes or so from cold (with percussive encouragement to the valve solenoid) then can't be got going again until cooled a while.

The valve's main solenoid becomes burning hot to the touch in that time, then presumably goes open circuit and stops. It also has a much lower resistance than the old possibly-not-so-broken valve. I deduce the solenoid coil must be partially fused and probably getting worse all the time.

However I can't explain the old valve thing.

Jon

[jms019]

I think I know why it has been running for ten minutes or so from cold (with percussive encouragement to the valve solenoid) then can't be got going again until cooled a while.

The valve's main solenoid becomes burning hot to the touch in that time, then presumably goes open circuit and stops. It also has a much lower resistance than the old possibly-not-so-broken valve. I deduce the solenoid coil must be partially fused and probably getting worse all the time.

However I can't explain the old valve thing.

Jon

[jms019]

Seems the main solenoid gets very hot to the touch then presumably goes open until cooled down again when I can start the thing up by smacking the valve to help it.

Jon