Why does my perssure keep going up?

[Onediyman]

Any idea why the pressure keeps going up on my combi boiler? I have a Vaillant Ectotec Plus about 15 years old. The heating has been off all summer and the filling loop taps are both fully closed but the pressure keeps going up. I empty about 2-3 litres of water from the system every 2-3 weeks. It's been like it for about 3 months.
The only thing I can put it down to is taht both filling loop taps and leaking water into the system but it seems unlikely for both taps to develop faults at the same time. As far as I understand, that's the only way pressure is going to get into the system. Am I missing something?

Any ideas?

 

[Deleted member 120897]

Does this go up after use, or does it go up without use? It could be the filling loop, easiest way to diagnose that one is to disconnect the loop. There could also be a pinhole in the plate heat exchanger, easy one for that is to isolate the cold main going into the boiler underneath, you‘ll have no hot water whilst this test is carried out.

 

[John.g]

Could be the plate heat exchanger (combi) leaking mains water into the primary circuit but I would disconnect the filling loop completely first to rule this out.

 

[Onediyman]

Does this go up after use, or does it go up without use? It could be the filling loop, easiest way to diagnose that one is to disconnect the loop. There could also be a pinhole in the plate heat exchanger, easy one for that is to isolate the cold main going into the boiler underneath, you,k have no hot water whilst this test is carried out.

Thanks for the advice. It's when it's not in use. I haven't used the heating since April and this started about June/July. I'll take on board the advice and come back if I need more help. Thank you.

 

[Deleted member 120897]

Thanks for the advice. It's when it's not in use. I haven't used the heating since April and this started about June/July. I'll take on board the advice and come back if I need more help. Thank you.

Do you use it for hot water though? Could still be the expansion vessel.

 

[Onediyman]

Do you use it for hot water though? Could still be the expansion vessel.

Yes, we use it for hot water. Could the expansion vessel cause water to leak into the CH loop? So, could it be a number of possible causes i.e. plate heat exchanger, expansion vessel, main heat exchanger...?

 

[John.g]

You might consider doing this first thing tomorrow morning while the system is cold, shut off the cold feed to the combi, at the boiler, if possible, if not, at the main isolation valve, open a hot tap to depressurize the plate heat exchanger, and leave open, check boiler pressure and if greater than 1.5bar, reduce it to 1.0 bar, fire up the boiler with all rads on, observe the boiler pressure when system up to full temperature, if the pressure is > say 2.7/2.8bar, then more than likely E.vessel problem.

 

[Onediyman]

Thanks John.g
I'll give that a try and see how I get on.

 

[EvilDrPorkChop]

Common problem on these at around this age, your filling loop is passing. You need to buy a new valve, ideally they both need replacing as obviously they're both passing but you can just replace one to save on the money!