Vaillant VCW-sine 18 T3 - Main burner does not fire up

[JimboEvans]

Maintenance History of Vaillant VCW-sine 18 T3
1986-xx Already installed when I bought the house. Thermometer permanently at 30deg
1990-xx PCB changed
2006-xx Realigned pilot light
2009-06Reconditioned diverter valve
2012-05Changed Drayton Timer switch Siemens Drayton
2012-05Replaced radiator TRVs & stop valves. Radiators flush.
2012-05Replaced piezo crystal ignition
2015-07Changed main heat exchanger. Slight burning smell
2015-08Flushed out Fernox protector. Main burner did not light for either water or heating
2015-09Differential valve cleaned. New diaphragm.

Detailed description of problem
The boiler is situated in one of our back rooms that we use as an office.

The main heat exchanger had a slight leak and was replaced with a new one. All was fine for the first few weeks, although there was a slight burning smell. The change in heat exchanger had almost solved the water leakage and I was advised to drain the system as normal to get rid of the sludge in the system but this time to add some Fernox leak sealant. After having done this and refilled to the normal 1bar, the main burner did not light for either hot water or central heating.

Thinking this was something to do with the sealant, I flushed the system and refilled with water. The main burner still did not come on.

The differential valve was cleaned and a new diaphragm inserted and the pin was checked to ensure easy running. The pump was opened and cleaned and its movement checked with a screwdriver. The rubber overheat button was reset.

The main burner still did not come on. The pump can be heard and the trickle of water through the system can be heard. This is the same noise I hear when the boiler is working properly.

Current Situation

I have been advised that it may be the DC-solenoid that is at fault and my best plan of action is to track down an expert on the Vaillant VCW-sine 18 or have a new boiler installed.

As long as it is not going to cost an arm and a leg I would prefer to retain the existing boiler as I have found it very reliable. I have tracked down a new DC solenoid (Vaillant part 111115) from AK boiler spares for £118, which I would be happy to buy if I could find an expert (I live in South West London).

Failing that, what would be a good replacement for the boiler and who would be a good installer?

Many thanks

 

[Phill Peck]

Best man for this job would be @Bunnyman but might be out of his area.
I think @Agile is also pretty knowledgable on this model and closer to your area.
It is a very old boiler but they are a well designed piece of kit enough to make most talk u into a new boiler

 

[Agile]

I have never heard of a solenoid failing.

But if I ever encountered one, I have two used ones available. ( Possibly three! ).

But I would never expect it to be the solenoid that has failed.

So what test has been done to diagnose the solenoid at fault?

For that matter, who did that diagnosis?

Tony

 

[JimboEvans]

Hello Tony & Gas Service

Thanks so much for replying.

No tests have been done to diagnose whether the solenoid is faulty.

However, the diagram in the servicing manual, 9.4 Sheet 4 p53, suggests that if the differential valve is working, then the DC solenoid should be replaced.

The person who looked at the boiler is now retired and I do not want to involve him any further, particularly as the problem may be difficult to resolve.

Tony, if the problem interests you and it is one you think you might be able to sort out, perhaps we can come to some arrangement?

Best wishes
Paul

 

[Agile]

It sounds as if these are totally guesses as to what may be wrong and not based on any proper diagnostics.

Do you know that the differential valve is working?

Changing a £116 part when no testing has been done is just plain mad for any service help. Before fitting any expensive part it needs to be tested to see why it is not operating. The first requirement is that it is actually being supplied with the correct voltage.

If you want to discuss me coming then you need to email me with the address in the subject line or text me but email is better. My contact details are in my profile you get by clicking on "Agile".

Tony

 

[JimboEvans]

Tracked down a local engineer via B & G. There was a problem with the automatic air vent on the pump(£20 to replace). Thermometer (£20) replaced at same time. Boiler works fine now.

Suggested replacement boiler: Vaillant EcoTec Pro24.

 

[Bunnyman]

That was simple then, lucky find with a BG man knowing that ..