valliant problem

[Mike13]

Well We have a Vaillant VCW GB 242 EH or 282 EH, it slowly looses pressure and also in cold weather the CH doesn't come on, even though the pressure is fairly normal. The key thing I have found is that changing the pressure by either adding or removing water will kick the heating into life again for 1/2 to 5 days in cold weather.
We had a plumber come round and between us we sorted out that it was around the diverter valve, which was leaking a bit anyway, so that has been changed, but this winter it has started going wrong again.

What should I do from here, Vaillant aren't interested in coming out the first plumber was honest enough to admit he wasnt that sure of the hydraulics in the vaillant.
I am comfortable with measuring pressures and flows as an ex designer of gas analysers, but don't have much pressure equipment available, but I do have a decent DVM and soldering Irons.

As a newbie on this forum I don't see where I get other peoples profiles from.

Mike
______________________
moderator

Welcome to the forum, may I ask that you read the forum rules. Your post has been split

 

[chrishutt]

Presumably you have studied the manual for this boiler, so you should now understand that the diverter valve is controlled by the servo valve, which is controlled in turn by the water (section) valve.

The control is mostly via small bore tubes which transmit differential pressures generated by the pump. An apparent problem with the diverter valve may in fact be a problem with some other part of hydraulic circuit.

As an ex designer of gas analysers, you ought to be able to work out the control sequence and test each stage of it. Watch out for debris blocking tubes and impairing servo movement.

 

[Mike13]

Hi Chris,

Thanks for replying, but the details I have in my possession (it came with the house) are not enough. Also I have no idea what the sequence is meant to be. There were no pneumatic servo loops in the instruments I worked on.

What does the servo valve look like?? and are there any tips on dismantling to gain access without damaging anything?? How do I recognise the water section valve?
My forte was the electronics, more than the mechanical, mentioning that was just to say I could cope with dismantling and or measuring a differential pressure, presumably at 1 bar.

Mike

 

[andsam]

I think Chris is spot on and it is probably sludge in the impulse tubes . I have often found the servovalve completely blocked.It is at the bottom of the boiler in the middle and is black with 3 tubes connecting to it.

 

[chrishutt]

Understanding the boiler hydraulics is very similar to understanding simple electrical circuits, just a series of switches and valves really.

But you really need a manual. Is it beyond your initiative to get one from Vaillant? If so, look up my email in my profile and send me your email address. I should be able to send a copy of manual back to you.

 

[Mike13]

Okey dokey, it looks like I have to dismantle any small tubes there and blow through them to see if anything is blocked.

Last year when it went wrong and I called out a plumber after many hours looking at the symptoms and all that, wasted many hours on the phone trying to get an answer from a vaillant engineer, I dont really want to repeat that scenario...

Mike

 

[chrishutt]

Mike, since you're in Surrey, you might be in the patch of ChrisR who posts on this forum. He is very good and certainly knows what he's talking about. You might find his email in his profile, or email me for it.

 

[Mike13]

Hi Chris,

Thank you very much for the pdf's, there was new information in there that makes me more confident about trying myself.

I also have e-mailed ChrisR for a backup incase I get stuck.

Mike

 

[Mike13]

Well an update, the pressure differential switch has sprung a bad leak, I have the replacement arrive today, but what I need to know is do I need to turn off the gas before I replace it? or is it isolated from the gas section?

Regards,

Also at the bottom of the boiler there is a knob that connects to a chromed section with several large pipes connected and has the spring loaded microswitch just above thisd piece. Well the problem is that the knob is stuck, does this matter, and what would I need to buy to repair this part.

Mike

 

[Mike13]

Hi,

I managed to change the pressure differential switch, so now it doesnt leak and the heating is working again.
The next problem is the servo valve just below it. The question is how do I get access to the back of it, how is it removed from whatever it is bolted to?
I have CH bet no HW, it runs tepid for a few seconds then nothing, if I fiddle round the back of the servo valve I can get the boiler to fire and the HW runs hot again, I am assuming the leak from the pressure differential switch has frozen or corroded something behind the servo valve and so need to remove it without breaking it.

Regards,

Mike

 

[Gasguru]

The diaphragm in the water section may have perished or become weak. Differential pressure on this diaphragm (when you open the hot tap) lifts the pin. The pin rotates the cam actuating the microswitch and setting the servo valve to apply the correct hydraulic pressure on the diverter valve.

A single screw secures the water section. Check the manual for the correct position of the switch and the adjustable pin. If you move the control box out it makes access easier.

You may also find the servo valve partially siezed. Some times the ceramic discs inside do not fully reverse the water flow (in effect they leak slightly) as the discs are not in perfect contact with each other. I have managed to rebuild the servo valves on previous occasions.

 

[Mike13]

The unit is at the back of a narrow cupboard, and access is uncomfortable, I managed to get the whole assembly out in one piece and cleaned it up as best I could outside, the single screw you refer too is corroded into place and I cannot get the screw out, I used naval jelly then plusgas, it is just opening out the screw slot when I try really hard.

The diaphragm was perished and had a small hole in it, it has been replaced. All that needs to be fixed now is the assembly that screws in from the front with a white plastic knob with a red thermometer sign on it, as described in my other topic I broke a thin plastic threaded rod internally.

Regards,

Mike