VAILLANT 20/1 T3 W WON’T SWITCH OFF

[Agile]

I always measure mains voltages from the terminal to the chassis as I find its less confusing when there is an electrical fault.

In this case it would often be a water section pin jammed out, a common fault, but you say the boiler does fire up when tap on.

In that case without being at the boiler I dont have any guesses to make. In any case I dont guess at boiler faults, I only diagnose by testing.

Tony

 

[gorselands]

Thanks for getting back. Thanks Bunnyman for red micro info. and as you said at the start, pointing to water section that I will look at tomorrow In meantime reassemble timer, and getting gray base on is a pig.

thebunny831 You seem to agree. To the layman what's S1, PPII, and OP?

'water section switches stuck on, flow switch rises, breaks S1. Boiler set to PPII, boiler sits there for a while with pump off, and thats when OP thinks its all OK.'

Does it need a drain down or will a bucket do?

Thanks again, Mike

 

[Agile]

The water section only contains 1/2 liter at most so a bowl is all that is required.

However, it does not need draining yet!

You need to observe pin moving and returning promptly.

Microswitches are checked electrically.

Tony

 

[The831Bunny]

Thanks for getting back. Thanks Bunnyman for red micro info. and as you said at the start, pointing to water section that I will look at tomorrow In meantime reassemble timer, and getting gray base on is a pig.

thebunny831 You seem to agree. To the layman what's S1, PPII, and OP?

'water section switches stuck on, flow switch rises, breaks S1. Boiler set to PPII, boiler sits there for a while with pump off, and thats when OP thinks its all OK.'

Does it need a drain down or will a bucket do?

Thanks again, Mike

That's tech talk for different parts of the boiler Mike

OP is original poster (that's you )

What you need to do now is turn off electric to boiler, take off terminal box cover, take out the 4 screws on the front of the aluminium control box, easing up slightly the red/green push button box. Pull the plate forward with the rocker switches on, and disconnect the A and B push on edge connectors. Leave mains wiring connected.

Look inside with a torch. As Bunnyman said, look for any water damage or corrosion, it may have damaged the front pcb.

On the base of the box will be a pair of red micro switches. The water section spindle should move up when the hot water tap is turned on, and down again when turned off. You will probably find it stuck up, and you can see 3-5mm of spindle. You can either remove the section and overhaul it, or replace the section complete.

When reassembling the box take care with putting the A and B connectors on correctly.
Hope that helps.

 

[gorselands]

Brilliant, thanks for that. After reading agile (Tony's) reply have been looking at how I could see pin move! After close inspection and an hour or so reading every post 'water section' was beginning to think it must involve looking inside CB. Will report back. I do appreciate all the help.

 

[Agile]

If you decide to remove the water section then you need a very good screwdriver of the correct size to fit the clamping screw as they are usually very tight.

I always refit with silicone grease to make it easier the next time. Pity others dont do that.

It always worries me that I might have to drill out and retap!

Tony

 

[gorselands]

Ouch! Where exactly is the clamping screw, is it the small one center directly under CB and could I WD40 it? Sounds like a job for my gold plated Snap On!

Mike

 

[gorselands]

Hi The831Bunny. Removed cover as per your instructions. The area around the pin is quite scaly (white powdery) and, if anything, appears stuck down as only about 2mm showing.

Gentle up with small screwdriver on contact spring operates MS's. Pin doesn't move. I think you say that with boiler off it should be up (3-5mm). So if it's not moving, this will be cause MS to remain on (off) in turn affecting timer operation.

Suspect MS's do more than this, I recall Bunnyman saying something like CH could be dumping into the HW or am I talking out of my 'heat exchanger'?

Mike

 

[gorselands]

UPDATE: After putting it back together (PCB looked fine, no watermarks), switched on boiler and it fired up. The timer was on constant so just tried it in OFF and boiler switched off! Tried it on timed and it's all working again. Could it have been a dry joint?

Rather than feeling delighted it's working I'm left feeling 'what's happened to make it work again?' I haven't done anything!!

Mike

 

[The831Bunny]

At least you are in the right area now

The curved metal plate below the microswitches should sit flush (NO spindle showing) with the top of the brass gland of the water section when the tap is OFF. It will rise 3-5mm when the tap is turned ON. This is the area of your problem. The corrosion/scale you are seeing is caused by the gland leaking and then drying up. As soon as you turn a hot tap on the spindle will almost defiantly stick up again causing the pump and burner to stay on and then the rads will warm up.

Quick cheap fix: lubricate the spindle with some silicone grease. It MAY help, but my monies on the problem returning.

Correct fix: Remove the water section and overhaul with a new gland, diaphragm, fixing kit, and washers (assuming you have a 14mm socket and it all comes apart) OR replace water section complete (your best bet).

 

[gorselands]

First thanks for getting back. I had to raise the plate slightly to see the spindle, definitely not flush but not raised enough at that stage to operate the MS. I did run the hot tap for a while and then switched CH on and all worked well. Switched off, left it and switched on again, still working.

You are right, the area round the spindle doesn't look good and I think problem may re-occur. My thoughts are to inspect the water valve and refurbish or replace. The diaphragm is available locally though I suspect, gland, fixing kit, washers will be harder to come by and so far, unable to track down part numbers. The valve is also available about £100.00 on the internet. Thanks to you and Bunnyman for guiding me to the problem area and for Agile's kind contributions.

Have all the tools from when I was a car nut.

Cheers for now, I will keep you updated.

Mike

 

[Agile]

I am again confused. You now seem to be saying the pin is NOT moving.

But previously you implied the hot tap did turn the boiler on which would imply the pin was moving ( assuming the preheat was off ).

Tony

 

[Bunnyman]

Let it go tony, as 831 said I would change the complete valve on a unit as old as this , refurb usually needs a bit of experience but u maybe ok as its all mechanical stuff,but this is a common fault as we have said and trust me it WILL return, change that red switch 126215 before it knackers the relay on the pcb, an make sure u get the wires right. If u buy a pattern one the tags are usually not the same

 

[namsag]

Agile use this thread as a lesson instead of trying to contribute .
Bunnyman is probably the top guy in the country regards sine boilers been doing them for over 25 years now from the days when no one would touch them.

Dont that make you feel old bunny

 

[Bunnyman]

1 day we must meet namsag