Vaillant VCW 20/1 T3 W PCB Problems

[gorselands]

As Max Bygraves used to say - "I wanna tell you a story.".

This week car electrics went. Yesterday dishwasher stopped working. Last night boiler packed in!

Saw there was a leak from diff. valve. Dismantled and cleaned pins/stuffing box (will get new diaphragm on Monday). Switched on - On/off switch on switch board glowed bright red and popped.

Removed switch board - both 2 amp fuses blown. Checked the PCB including resistor and all seems OK. Obviously water somewhere. Can't dismantle switch box but have managed to get cover off ON/OFF switch - Funny bulb with a small resistor wired in. Can't find any reference to the bulb. Does anyone know the part number of the bulb and whether or not it affects the boiler working?

Any help gratefully received

Mike

 

[Agile]

It is only an indicator but I dont think it is available as a spare part except as a switch assembly!

Its only a neon bulb with a series resistor but would not usually ever blow as they are not that sort of bulb! If it can be opened can be replaced by someone with electronics experience but its only an indicator and does not affect boiler operation.

Tony

 

[gorselands]

Thanks Tony,

Will leave it and replace the 2 amp fuses and see what happens.

What's your advice on draining the boiler to work on the differential valve?


Mike

 

[The831Bunny]

As Max Bygraves used to say - "I wanna tell you a story.".

This week car electrics went. Yesterday dishwasher stopped working. Last night boiler packed in!

Saw there was a leak from diff. valve. Dismantled and cleaned pins/stuffing box (will get new diaphragm on Monday). Switched on - On/off switch on switch board glowed bright red and popped.

Removed switch board - both 2 amp fuses blown. Checked the PCB including resistor and all seems OK. Obviously water somewhere. Can't dismantle switch box but have managed to get cover off ON/OFF switch - Funny bulb with a small resistor wired in. Can't find any reference to the bulb. Does anyone know the part number of the bulb and whether or not it affects the boiler working?

Any help gratefully received

Mike

Best to change the black plastic PDV as a whole part if its leaking. Part No. 151017. If its chromed brass, then changing the gland and diaphragm is worth it. Water from the leak usually drops onto the aluminium control box straight through to the front PCB and takes the 2 amp fuses out. Dry out the switches and PCB with a hairdryer. Also check the edge connectors to the PCB are connected to A and B correctly, and the water section switches on the base of the box are dry.

There are more T3W's working with a duff neon then a lit one

 

[Agile]

If you mean the water demand valve underneath that will only prevent a demand for water firing up the boiler. But it will still provide heating.

It will also heat water if the water preheat position is used !

Tony

 

[Agile]

If you mean the water demand valve underneath that will only prevent a demand for water firing up the boiler. But it will still provide heating.

It will also heat water if the water preheat position is used !

Tony

 

[gorselands]

Thank you Tony and The 831 Bunny,

And thanks for the part number. Will let you know how I get on.

Mike

 

[gorselands]

Just a thought, what's the best way to drain boiler to replace diff valve? Close off the two isolating valves and open bleed nipples?

Mike

 

[Bunnyman]

Yes

 

[gorselands]

Thanks Bunnyman,

Mike

 

[The831Bunny]

Yes

Will you stop it with your in depth, over complicated advice Bunnyman

 

[gorselands]

Update: Electrics all working inc. neon switch.

Have just got new black plastic PDV . Couple of questions - I thought the two small water pipes would be threaded but see they must be a push fit held in by the securing plate. Do they need any sealant ? And is it necessary to drain the boiler or could they be transferred to the new PDV with a bowl underneath?

I ask this because I read somewhere on the forum that the boiler isolating valves can weep and should not be disturbed if possible. On inspection one of the valves seems to have weeped in the past but is dry now.

I am away tomorrow for five days and will do the job next week.

Many thanks

Mike

 

[Agile]

You need to ideally lubricate them with silicone grease.

In theory you need to isolate and drain the boiler.

But many would successfully just depressurise the system and accept a little water leaking when it is changed.

But whatever you do you should use plastic sheets with a towel under to try to prevent any water getting onto the electrical parts.

When repressurising the boiler it helps to have the auto air vent behind the pump working properly.

It can take a while to get all the air out.

Tony

 

[gorselands]

Thanks Tony,

What's the best way to depressurise the boiler other than the using the pressure valve (again, I've read this can weep).

The automatic de-aerator looks pretty green round the edges and is probably why the rads want bleeding from time to time. Will loosening/taking off the small cap be sufficient or is that another part that will need replacing?

Mike

 

[gorselands]

Back from 5 days in Cornwall, hence delay in posting.

Have just replaced PDV valve, pressurised system, bled heat exchanger and removed cap from auto air vent behind pump - very slight bubbling/sound of air.

HW & CH still not coming on so suspect and can see diapragm pin not fully extending. Tony says "It can take a while to get all the air out".

Is there any more I can do? Also bled pump. Everything else seem fine.

Thanks

Mike