Vaillant Ecotec boiler losing pressure intermittently

bris

Trace the pipes up to the boiler, there will be 3 22mm valves, 2 for flow and return and 1 for gas. Turn the flow and return off. Make sure its pressurised before doing so.


P.s don't try and use the heating with the valves closed.

Alex1983

It’s unlikely to make any difference, the only 2 places it can leak in the boiler is the PRV and the heat exchanger and seeing as they’ve both been done it’s looking like a issue on the system.

How many radiators do you have?

Alex1983

Also might be worth going back to basics and capping the under floor off just in case one of the isolation valves is passing.

BillG100

Thanks. I've just spoken to Vaillant and they told me an F.75 error is usually a problem with the Pressure Release Vessel rather than a leak in the system which normally generates an F.22.

I explained there was no sign of water from the overflow pipe so if that is the case where could the water be going. They said the Pressure Vessel (?) holds approx 1 gallon of water and it won't release until full. As I only need to add a small amount of water (a second or two of the tap on) into the system every couple of days it may take a long time to fill.

Does that make sense / sound plausible? I would have assumed the BG engineer would have checked whether there was water in the pressure vessel but perhaps he didn't. Anyway BG are sending out another engineer (it's on homecare cover or whatever they call it) in a couple of days.

If the pressure vessel is ruled out I'll then isolate the boiler as discussed above.

Alex1983

Pressure vessel is the expansion vessel which will be charged to 0.8bar of air pressure I think on the Vaillant, it will be printed on the side of the vessel.

F75 means the boiler tried to fire up but the pressure sensor didn’t detect the increase, it means a problem with the sensor/ pump or water pressure. If your topping up a lot your losing water.

The pressure sensors are temperament when they have dirt in them, I’d be surprised if they haven’t changed it all ready, you say they checked the vessel and replaced the heat exchanger. This only leaves a leak at the pressure relief valve or on the system.

BillG100

The latest update to the saga is:

1) BG seem happy the UH is isolated (valves not passing)
2) They have now changed the schrader valve on the expansion vessel
3) They said the pressure sensor (the one which provides data for the digital display) was faulty and have changed it

Of course even if 2 & 3 were causing problems it doesn't explain where the water was going as the overflow pipe is completely dry!

If the problem is still present after making the latest changes (will know in a couple of days) they will send the leak specialists in with thermal imaging / inert gas etc.

mossy007

Can you please let me know how you got on. I have the exact same issues with my same system UFH and CH and losing pressure intermittently some days few days some days overnight. We have had numerous visits from Baxi who have changed PRV and expansion vessel. When PRV was replaced the pressure held for 5 days and then lost pressure, more consistently overnight now. We are tearing our hair out at the moment.

BillG100

mossy007 wrote: »

Can you please let me know how you got on. I have the exact same issues with my same system UFH and CH and losing pressure intermittently some days few days some days overnight. We have had numerous visits from Baxi who have changed PRV and expansion vessel. When PRV was replaced the pressure held for 5 days and then lost pressure, more consistently overnight now. We are tearing our hair out at the moment.

Problem isn't fixed so leak detection are coming in with thermal cameras / acoustics / inert gas. We know the water has to be going somewhere but it is proving very difficult to determine where.

vickthestick

Thanks for all of this.
This is exactly our difficulty as well, minus the Underfloor Heating, but plus leaking radiators once the boiler cuts itself out - they don't leak if the system is pressured up.
Engineer out to take a looky-see tomorrow.
Please let us know how you get on.

BillG100

British Gas supposedly escalated the problem to leak detection on 3rd January but they've still not contacted me to make an appointment. I've already chased twice and been told they are on the case. Not impressed at all by the level of service!