Water Pressure in Central Heating

[Ergin]

Hello, I have a Vaillant Ecotec Plus Boiler. Every time after the heating has been on, when the system cools down I notice that the water pressure increases slightly. Yesterday I emptied the system to show 1.3 bar, yet after the heating system had been on that night, the next morning when the system was cold the pressure was showing 1.5 bar.
A week or two previous I had experienced a fault on the system, so I changed the water pressure switch, which fixed that fault, and at the same time I checked the Expansion vessel which was at zero and so I re-pressurised that to 0.8.
I cant figure out why there is water pressure increasing? Thanks

Ergin

 

[flameport]

Most likely the filling loop is still open slightly, or one of the valves is leaking.
Remove the filling loop to find out.

If pressure still increases with the loop removed, the problem is elsewhere and will most likely be expensive to fix.

 

[MANDATE]

Well its got to be coming from somewhere where the pressure is higher.
As already stated the filling loop if still connected is letting water pass across.
The other source will be a heat exchanger.Cold water at mains pressure enters the boiler and goes through a heat exchanger and comes out hot at the tap. If the heat exchanger is perforated in any way water will pass from the higher pressure side (mains pressure) to the lower pressure side (heating system) The flow across will only cease when pressure on both sides are equal, so the system side will creep up.

 

[dreadnoughtheating]

If all that fails, hunt high and low for another (forgotten) filling loop perhaps hidden away in a cup'd (ecotec plus has its own integral filling loop), and disconnect/remove it.

Dreadnought

 

[Ergin]

Thanks for the suggestions. The filling loop is the integral type with a valve on the mains cold water side and another on the central heating entry side, so I'm finding it hard to understand how this could be letting in water as that would suggest that both valves are faulty. Ive closed and opened both a number of times to make sure that there is no obstruction and that both move freely and snap into place, so to speak. Is it still worth replacing? and which bits of the filling loop? If it is the heat exchanger Ill have to seek out a gas registered plumber. Thanks Guys.

 

[RickyLee53]

Is the pressure always increasing. Or does it just change when its changing temperature?

 

[Ergin]

Hi, The pressure seems to increase slightly after the central heating has been on. On Wednesday 19th I drained system slightly so that it was at 1.3bar and by Monday 24th it was at 1.7bar. I did'nt have the central heating on too much as the weather was mild. On one day previous to this when I did not have the heating on at all during a 24hr period I noticed that the pressure did not increase at all. Thanks.