Vaillant ecoTECH plus 837 losing pressure.

[Antony2008]

Hi everyone.

This summer, I fixed a leak on a towel rad and had to re-charge the CH system. A couple of days after this, the boiler lost pressure and generated fault code f22. I also noticed water on the floor below the boiler and found a drip forming on the PRV pipework just below the boiler. The PRV'S external lock nut surprisingly was loose (around half a turn needed to tighten it). The boiler was OK for a couple of days, then again lost pressure totally. There was no water below the boiler, but I could see that the PRV must have activated as there was a water mark at the external outlet of the PRV pipework outside. I found that the filling loop had been leaching water into the CH system - the flats in one of the plastic taps had rounded, so while the tap was 90° and showing closed, the valve hadn't totally closed and was slowly passing water. I remade the flats in the plastic tap, recharged the CH and the boiler seemed fine for the rest of the summer.
With the recent cold snap, the wife set the CH timer... . Now, when the CH is called for, the boiler heats over a period of several minutes, with the pressure rising from 1.0 bar to 3.7 bar, at which point the PRV opens and empties the CH system, generating fault code f22.

As the boiler works fine for DHW, would I be right to suspect that the previous over pressurising has compromised the CH system with the PRV needing to be replaced, or is there more to it than that?

Your advice/recommendations would be greatly appreciated.

Antony.

 

[terryplumb]

Your expansion vessel isn't functioning as it should ,may just need to be recharged ,or it may be duff.

 

[Antony2008]

Many thanks terryplumb for pointing me in the right direction.

Yesterday evening, I Finally got round to checking the expansion vessel, which had no air whatsoever.

After isolating then emptying the CH of the boiler (around 7.6 litres came out, the majority of which I guess would have been in the diaphragm in the expansion tank), I recharged the expansion vessel to 0.9bar (as per installation manual) and left it for half hour with the drain valves still open on the CH (I thought this would prove the integrity of the diaphragm and expansion tank). The 0.9 bar was still present, so closed off the drain valves, opened the isolating valves and set the CH pressure to 1.0 bar while cold. On firing up, the boiler's digital pressure display showed 1.3bar, rising over several minutes to 2.2 bar as it approached setpoint of 65°C, remaining stable at 2.2 bar until 70°C, 10 seconds after which the gas valve closed. This heating cycle repeated after the temp gauge dropped to 55°C (with thermostat still calling for heat). After three of these heating cycles, the boiler seemed to be OK (though I thought that the burner would turn off perhaps a few minutes after setpoint, rather than 5°C above setpoint which takes several minutes).

This morning, the CH still has 1.0 bar while cold and no sign of discharge at the PRV. Hopefully none of the parts have been compromised after being over pressurised earlier this summer, and the boiler will be fine for years to come.

Thanks again terryplumb.

 

[terryplumb]

Your welcome mate.