Valiant combo pressure keeps rising

These things just happen sometimes. Nothing you've done, it's not a part you can break. It's leaking from the mains into the heating system.

As for cost, it depends on which version of the 831 you have and how long your warranty was (and whether you've had the boiler serviced every year). IIRC five year warranties were common when yours was fitted, in which case provided you've had it serviced annually it'll be free under warranty

If you haven't had it serviced annually, or it's not under warranty for some other reason, budget £200-300 depending on exactly which version of the 831 you have and where you are in the country
 
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I think it's too much of a coincidence that something goes wrong first time I dabble with it all after 4 happy yrs! I appreciate that I shouldn't be able to break it though...

Just wondering if it is worth running the heating, whilst not using hot water to c if pressure rises? Dunno what that would mean though if the pressure did rise. Am I right in saying that when the hot water is turned on a valve or something channels the ch water into the heat exchanger for the heat to be transferred to the mains hot water side of the heat exchanger, and that when I turn off the hot water, the valves are shut so the ch water is not routed into the exchanger? I'm just trying to work out what is causing the dribbling noise I mentioned earlier(3ish second bursts, happening much more regularly since the pressure rising started, but nothing to do with pressure maxing out and release valve opening I pressume as it system hasn't got above 2.6 bar yet) as it maybe a different problem..
 
No the waterways of the secondary Hex are always full. Just using the heating will not stop it. All the diverter does is change the flow of the hot water produced by the primary Hex. The pressure will still rise regardless.

As said before just get someone out to confirm diagnosis. This is what I love about this forum, people ask for advice, you give them good advice and then still question it as it's not the answer that they want or it isn't a free fix!

Jon
 
Jon I've appreciated the help as I've said already. Also, can u point out from my last thread where I questioned advice? I just wat to understand better as I'm interested. And anyway if I hadn't questioned someone's advice at the start of this I would have replaced my expansion vessel for no reason? Seeing as u r on here giving free advice I would have thought you'd appreciate someone interested to learn more?
 
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I wonder if the op has more than one filling loop as its unusual for someone to disconnect the internal one.
 
I wonder if there is a leak from the valve between the cold mains in and the filling loop? I checked and nothing, but there was a small leak from the valve between the hot water return and the filling loop, and I'm wondering if, when hot water fills the filling loop and hits the valve at the mains side this causes expansion somewhere and therefore water in from mains side... I'd like to try this out by disconnecting the filling loop but how would I do this if there is a leak at the hot water out end?! Still going for that cheap fix jon ;) This would tie in with the fact that it bggered up after I had mucked about refilling the boiler via the loop for the first time ever, i.e. turning those valves for the first time in years. Then again, the whole CH system pressure dropped to practically no pressure due to leaking rad valve, and I wonder if this meant more strain on the heat plate in the heat exchanger due to a big pressure difference at that point... I'm getting a kick out of this. I didn't realise how empty my life was without boiler fun and games. I won't be saying this when I have to shell out the cash though..
 
@jp butterworth could you post us some pictures as you stated that you had already disconnected the filling loop! There should be caps attached to either side of the loop to stop any leaks. If they are missing then you need a couple of 1/2" blanking caps.

Could you get a pic of the underside of your boiler as there is an internal loop in there, One from the front showing the pipework arrangement and one of the filling loop that is leaking on the hot side.

For the previous test to have proved anything you would have needed to remove the silver braided section of the loop (if you have one.) A few pics will be able to clarify alot.

Jon
 
My sister had one of these go on a Vaillant Ecotec 831 last month, 2 months out of the 5 year warranty.
The original fitters came and charged her £285 to replace.
They had sent someone the week before to do the annual service and it cost £90, it was a young lad who was there no more than 20 minutes. She mentioned the rise and fall in water pressure, and the guy doing the service said he didnt have a clue and wasnt there to diagnose or repair, just to service. His advice was to ring up and book an appt.
Am not sure what she actually got for her £90 service, a poke around with a screwdriver by all accounts.
Its out of warranty now so she feels that she doesnt need to spend £90 a year with that mob -just to get a stamp in her book. i dont blame her, advised her to go elsewhere.
 
@BertieC You don't have to have services carried out by the original installers just to keep the warranty. Any independent RGI can service the appliance just ensure that the Benchmark book is completed and the warranty will remain valid.

£90 for a service in the London area is far from expensive.

Jon
 
Yes u r right I did say that I had disconnected the filling loop to check for leaks but seeing as thre wasn't one from the cold mains side I re attached as the ch out side was driPping.

Image

Image


The ch out is far left, with the filling loop attached on Lhs of that. I unscrewed the filling loop from the other end, the mains in end. There was a small dribbling leak coming out of the filling loop unattached end which was continuous so not residual loop water. There was no drip coming out of where the filling loop had been attached to at the mains in side, so I assumed the filling loop was not a prob (mains water was not isolated when I checked this). Hope the pic is clear enough.
Cheers
 
Latest news : there is a very small leak coming from the cold mains into the fill loop. 1 drop every 5 seconds. There is a slightly bigger leak coming from the ch flow side of the fill loop (had said ch return before but realised it's the ch water out the boiler not that it really matters or does it?) about 1 drop every second. I think I didn't spot the leak on the cold mains side of the loop as I unscrewed the fill loop at that side and so the small leak probably would have spilled out and trickled down the back of the copper pipe where I couldn't see the blighter. This time I've unscrewed the fill loop at the non cold mains in side so can see the dripping out of that easily (not just residual water). So, not really understanding fluid mechanics myself, if the pressure is more from mains side but leak is smaller, will this force water into ch flow if leak from that side is bigger. My intuition says yes? I bleed the rad of about 2/3 litres every 3 days, so could imagine a drip every 5 seconds amounting to this. I guess the flow would be checked by the ch flow pressure to some ratio though. This would explain why this prob arose after turning these valves for first time in 5 years. The seals have gone? So, apologies for wasting time guys I just couldn't see the leak. Totally right to assume heat ex without this knowledge! Shout if u think I'm right Jon! Don't leave me!
 
Yes change the loop, it's a known problem, an do it quick, ur constantly filling over the last few weeks with fresh oxygenated water, your system will be slugding up
 
Cheers Bunnyman. Do I need new valves or is it just a washer or something? Vaillant 831 ecotech
 
Is there a chemical I should put into the system once I've fixed the leak to de-sludge?
 
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