Vaillant VCW Sine 18, hot water problem

[Roger60]

Hopefully one of you expert guys can help me with this one. The boiler will not fire up when a tap is opened, with the RH switch in the instant position.

The water section diaphragm has been replaced (was knackered), pin works fine; the pair of microswitches which the pin operates has also been replaced. The switch pcb has been replaced as it had a small burnt section. CH works fine, and 'warm start' DHW works well, so we are relying on that at present.

What else could be the cause? I've read that the diverter valve wax stat could be the culprit. Are the other microswitches a possibility?

Any help gratefully (and graciously) received.

Rog

 

[DP]

Roger can supply that section. Most likely the section near the silver tank

 

[Roger60]

Is that the whole valve, or just the wax capsule? I'm sure the valve will cost, and I'd like to be more certain I needed that as opposed to the capsule.

Thanks.

 

[Roger60]

Been researching some more - I wonder whether the pin at the top of the diverter valve is sticking and/or the microswitch there is working properly.

Gonna investigate tomorrow, only problem is my boiler is snug up against a wall on the left - not my handiwork I can assure you!

 

[Bunnyman]

In Npton as well these boilers ceased production 1986 so at least 27 years old so it's done well, they were great units. If ur sure water section is lifting and makin both switches then I would suspect diverter valve ( flow switch) . However if the the warmstart is working when heating switch is turned off this would mean the switches are working correctly. I would turn ch switch on boiler off, put warmstart on an see if boiler fires for 15-20 secs . This would prove the diverter lifting. Check the overheat switch rubber button on rhs of the alloy box . I won't go into the wiring now but it can cause this fault if its wired wrong if its tripped, the heat will work but not the hot water

 

[Bunnyman]

Ps wax capsule 140106 and diverter 141001 both now not available so ur stuffed unless u go second hand

 

[Roger60]

From your advice Bunnyman it appears that the diverter is OK. CH set to off, warmstart on (which is what I was using anyway for DHW) and yes it fires up and presumably is filling up the reservoir within the boiler. It refires every time I draw hot water, so that seems OK.

Pushed the overheat reset, didn't appear to have operated, and made no difference.

Could it be the differential valve microswitch? Any other thoughts? What wiring options are there - I'm not aware that any connections have been tampered with.

Guess I might have to live with using warmstart for the rest of its life - another 27 years, maybe - will outlive me then . Come to think of it, I must have a reset button on me somewhere - now, where's that human body forum . . .

 

[Bunnyman]

Can u see the microswithes being operated in the alloy box when u open and shut the tap?

 

[Agile]

At that age its quite common for the micro switches in that boiler to be mechanically operated but due to oxide on the contacts not to make the circuit.

They should be measured NO and NC to ensure the contact resistance is less than one ohm.

Tony

 

[Roger60]

I think I've found the problem. The water section diaphragm was replaced, and although it seemed to work, I can now see that the pin is not rising very far, and only if a tap is opened quickly and fully. So I diagnose a sticking pin, which I hope I can replace with a new one and a stuffing box.

Anyone agree?

 

[Agile]

It easy enough to manually operate the switches when taking hot water!

Tony

 

[Bunnyman]

Not likely, more likely the flow governer in the bottom of the water section is knackered, search ebay 011198 or 011156 change the section

 

[Agile]

It easy enough to manually operate the switches when taking hot water!

Tony

I mean just on test to prove your theory!

Not for the rest of your life or the boiler's whichever comes first!

The glands can be stiff but should have been felt to check when the diaphragm was changed. They can be lubricated with silicone grease.

Tony

 

[Roger60]

Bunnyman,

Not sure what the the flow governor does - it looks in the diagram like a restrictor? If so, then it could be furred up and restricting too much - is that the scenario, in which case I could clean it up? Or does it actually break in some way?

Appreciating your help on my problem!

 

[Bunnyman]

No its part of the water section change it is my advice, u can try cleanin the pin sn gland thats possible , try that first but my hunch without seeing it is changr the section i said