Boiler slowly gaining pressure over time

[demontec]

Evening,

I have a 5 year old Valiant Ecotek Plus 937 boiler. It is serviced annually and has been fairly problem free over the years.

I noticed that the CH system was at 3 bar and so called in a local plumber to have a look. He ended up doing a full chemical treatment, replaced one of the expansion vessels (smaller one), drained it down fully and then refilled it and treated it with inhibitor (over 2 separate visits).

The boiler is still gaining pressure at about 0.1 bar a week. I drain it down a bit to keep the pressure in a safe zone and if I leave it, it seems to peak at 3 bar and I can only assume it de-pressures itself via the PRV.

To fill it has 2 valves and so I don't think it is a leaking valve as it increases slowly and the chances of both failing don't seem viable.

I can't think what else it could be that is resulting in a slow increase in pressure a d so hoping some of you clever lot may have an idea.

Any ideas? Happy to call in another plumber but having spent a small fortune on the 1st chap who doesn't seem to have solved it, I am hoping for a steer initially.

 

[ianmcd]

Sounds like your Plate heat exchanger is pinholed

 

[demontec]

Damn, that is where my research had led to also. Before I replace that expensive part, is it possible to be anything else? Could air be getting in the system and getting stuck and hence increasing the overall pressure? I have bled all the radiators and they were all good so I suspect the answer will be a no.

If that is the only other viable option versus a leaking filling loop then I guess I may just have to go ahead and swap it out. With heat exhcanger plates, is it important to buy a genuine Vailiant part or are other cheaper options ok?

 

[Johntheo5]

Before you rush off and do anything, break the link between those two filling valves, if a flexible hose remove one end and see what happens, some combi boilers have a more permanent arrangement, it doesn't matter, break it.

 

[demontec]

I will have a look under it tomorrow and see how it's connected. I think it's a rigid fitment rather than a flexible hose. The reason you are saying to do this is to validate that there isn't a small continuous flow through the filling loop and by disconnecting it will show if water is coming through right?

 

[Johntheo5]

Correct, assuming you have a 12L expansion vessel then a increase of 0.1bar = ~ 0.37L, or 370ml in a week which only requires a leaking drip of only 2.2ml/hour, rule it out. Are you sure its only 0.1bar/week, if your normal cold pressure is 1.5 bar then it would take nearly 4 months to reach 3.0 bar and PRV release.

 

[demontec]

The 0.1 bar was a complete estimate and it is probably a little more in all honesty. I will check the loop tomorrow and measure the increase a little more accurately.

Thanks for the help and I will report back with any findings.

 

[ianmcd]

Could air be getting in the system and getting stuck and hence increasing the overall pressure? I have bled all the radiators and they were all good so I suspect the answer will be a no.

Nope air in the system would not make any difference whatsoever, if your system pressure (primary pressure) is increasing, it can be an expansion problem, but if this was the case you would be constantly topping the pressure up, if you are not then mains pressure water is getting into the system water somewhere, this can only happen via the filling loop or the plate heat exchanger, remove the filling loop to rule that out (WRAS regulations say it should always be removed anyway) but we wont get into that, if you want to test if it is definately the plate heat exchanger, test how long a period of time it takes for the pressure to increase, say 24 hours it increases by X amount, then next day isolate the cold water inlet to the boiler and leave hot tap open (obviously you wont have any hot water) if the pressure doesnt increase then it is your plate heat exchanger that is the problem

 

[ianmcd]

Correct, assuming you have a 12L expansion vessel then a increase of 0.1bar =

While I do enjoy your postings and all your calculations the boiler in question has a 10L expansion vessel so never assume , re-calculate

 

[Johntheo5]

Don't think its of earth shaking consequence in the above context as a increase of 0.1 bar results in 0.28L increase in EV fill volume vs 0.37L with a 12L, of course yet more assumptions must be used ie a precharge pressure of 1.0 bar and a filling pressure of 1.5 bar, if, for example the precharge and fill pressures are both the same at 1.5 bar then a increase of 0.1bar results in a 0.38L increase in EV fill volume with a 10L EV, again no big deal in the above.

 

[demontec]

Hey,

I have disconnected the filling loop today and tbh, I think this might actually be the culprit. I disconnected the end that connects to the CH (smaller connection end) rather than the end that connects to the cold water feed.

Both were dripping, the CH side had a small drip from the valve where I disconnected it which when I tightened the grey handle, has seemed to stop but the end that is still connected to the filling loop hose has a very slow but constant drip. I have left it for a few hour hoping it might just be residual water in the pipe but it's definitely continuing.

The problem I have is the access under the boiler is very tight and so replacing the valves is going to be a nightmare.

What options do I have hear and are there any you would advise over the others? Sounds like this is quite a recurring theme on these boilers sadly.

I believe one end of the loop hose is 1/2 in size and the other end is much smaller.

Thanks for all the help so far on this. Really hoping I can sort either myself or get someone in with a specific ask rather than needing them to investigate further.

 

[demontec]

 

[demontec]

 

[Johntheo5]

The filling loop should be disconnected anyway after top up, why not put a blank on the end. If the more important boiler side starts dripping you can probably get a female blank for this.

 

[demontec]

That is going to be quite difficult as the access is pretty awful. I have read about capping off this loop and doing an external loop to make it easy access wise and remove what appears to be an underlying issue with this boiler. Is that viable? I was looking at this old thread - https://www.diynot.com/diy/threads/valliant-ecotec-filling-loop-leak.401114/ but I am struggling to follow exactly what would be needed. It was for a different model ecotek so that may be why I am struggling.