Vaillant Expansion vessel charging/failing?

[ThatUKDiyGuy]

Hi folks

We have a Vaillant ThermoCOMPACT 637. It is about 8-9 years old.

When using the heating for the first time last week I checked the boiler and noticed that the pressure was nearly zero.

Having been reading various threads here and from watching the boiler this morning I think I have gotten close to the problem.

When the pressure is 1bar cold and the heating/boiler comes on I saw the pressure almost at 3 this morning - I wasn't watching it all the time so it may well have hit 3. The PRV pipe is hot so suspect it has opened. After just one hour and reaching about 70 odd deg the boiler went off and the pressure was 1bar (hot) and then fairly slowly dropped away again. It is now back to almost zero again.

Our boiler seems to run with little pressure so it may have been low for quite a while during the summer. The hot water on reflection wasn't as hot as it is once the pressure is topped up, which makes me think it has been like it a while. I've not been topping it up at all during the summer but last winter I had to top it up fairly frequently when we were using the heating - every 3-4 days maybe. I thought it was a slow leak.

I'm no expert at all but from reading lots it points to the expansion vessel either needing a recharge or is failing/failed. I see that you can test the Schrader value for water. I also read that vessels last around 10 years, which if true means we're fairly close to it.

My question is really should I be able to do this myself (re-pressurise the vessel) or should I be calling somebody out (e.g. Vaillant) to do this and/or fix/replace. We had Vaillant out before and it was £300! but, from memory, I think they covered expansion vessels in that charge - would need to double check. I guess what I'm trying to mitigate is if it just a EV re-pressurisation then paying £300 doesn't feel too smart but maybe paying that call out for them to come and do a full EV repair might make economical sense. Also, if the PRV has been opening a fair amount then again from what I've read maybe this needs replacing too and should you expect somebody like Vaillant service to do that too?

Many thanks

 

[Agile]

You have written a lot there.

But all those questions are covered in the FAQ and Wicki parts of this site in the pinned topic list.

Read them and they should answer all your queries.

Unless expensive parts are needed a local independent is always cheaper, usually much cheaper.

Tony

 

[denso13]

//www.diynot.com/wiki/plumbing:faq:faq7

 

[ianmcd]

it is easy enough to do it yourself and all you need is a car tyre pump with a guage on it, but follow ALL the instructions in the WIKI it wont work unless you do you cant just pump it up without opening a drain point somewhere

 

[ThatUKDiyGuy]

Thank you so much everyone for your responses. I've read through the FAQ and it makes sense on the whole. I just have a couple of questions:

- When opening the drain point do you need to open all valves up on the rads and then open the bleed valves or can you just literally open the drain point and draw off 10 litres and then shut off the drain?

- I'm a little bit confused around the pumping up process. I see that you pump the PV up to 0.7/10psi initially. You then remove the pump and put it back on again and the pressure should drop a bit. You then you repeat this process, pumping back up again to 0.7/10psi? When do you know when to stop? The wiki says it is "IMPERATIVE that water or air is allowed to escape from the heating system as it is pumped out of the PV" - is this covered by the initial 10 litre draw off - you're creating the space for this by draining the 10 litres out - is that right? So are you looking for the point where you put the pump on and the pressure is stable at which point you can drain off another 10 litres and if the pressure is still right you're done, else you repeat the process - is that right?

With regards to the PRV which has opened quite a few times I suspect. Can I address this after taking care of the PV as a separate job? From what I've read you can just isolate the boiler to do this. Is there any chance at all that the PRV might not be shot?

Thanks again

 

[ThatUKDiyGuy]

Update: I have located the air valve - it is right at top of the boiler - it released a tiny amount of air but no water, which is great news.

 

[Agile]

That 10 litre part is not a good bit of advice. I would like to rewrite that section.

All you need to do is to keep some part open ( any bleed screw will do ) as that's needed to expel the water pushed out of the exv as the air part becomes pressurised.

Ignore the 10 litre part.

Tony

 

[ThatUKDiyGuy]

Thanks for that Tony.

Did the PV today and all went OK.

Boiler is now no longer hitting 3psi and seems much happier now around 1.5 at 75deg. I monitored it for an hour and the PRV pipe seemed to remain cold the whole time.

Will monitor the system for a few days and fingers crossed no more pressure drops.

Cheers

 

[Agile]

A plastic bag or condom tied on the PRV discharge pipe is the tested way to see if any discharge.

 

[ThatUKDiyGuy]

Hi there Tony

Been keeping an eye on the pressure but looks like still losing a small amount now. I pressurised to 1bar yesterday and it is now just under 1bar.

The boiler is in the loft (don't ask!!) and the PRV pipe exits pretty high up so I'd rather not get up there if I can avoid it. I think I'll just replace the PRV if that is easy enough to do. It must have opened far too many times in the past year.

This is the valve:

Untitled

• ThatUKDiyGuy
• 16 Oct 2013
• 1

Untitled

• ThatUKDiyGuy
• 16 Oct 2013
• 1

Pretty sure it looks like it is Vaillant #190732 (boiler is thermoCompact 637E)

There are quite a few on ebay although not entirely sure if I'd trust that. Can be found on other more reputable sites - open to recommendations if that's allowed on these boards.

http://www.ebay.co.uk/itm/VAILLANT-PRESSURE-RELIEF-VALVE-190732-/290996404008
http://www.ebay.co.uk/itm/Vaillant-...ressure-Relief-Valve-PRV-190732-/330671680029
http://www.gas-spares.co.uk/Catalog...-Aquaplus/PRESSURE-RELEIF-VALVE-3bar-Cw-elbow

Is this fairly straight forward to replace?

Found a similar question on another forum. This is my surmising of what was said:

- Release system pressure
- Turn boiler off / isolate electrics
- Isolate valves on boiler (left and right pipe turn valve half turn - middle pipe is gas)
- Unscrew bottom of PRV
- Remove the clip on the elbow (I think it's called that)
- Unscrew valve anti-clockwise (have bucket ready)
- Silicon grease on the threads?
- Screw on new valve
- Replace clip

Thanks again