Combi Boiler Pressure Dropping

bassamnz

Hello, I was hoping you could help me identify what is causing the problem with my Viessman Combi Boiler. It is a Viessman VITODENS 111-W. Type B1LA. Gas condensing and storage Combi Boiler.

The Pressure drops to below 1 bar and the boiler refuses to turn on. So i re-pressurize the boiler to about 1.5 and reset it which gets everything working again. I was watching what happens and this is what is occurring.

1) When the House gets to my desired temperature, the boiler cuts off.
2) Then when the temperature in the house drops, it kicks back on. When it kicks back on, The pressure initially drops about 0.2 bars and then climbs back up about 0.18 bars. This happens suddenly. 2 very distinct movements in the gauge to drop and climb back up. (Note that when it climbs back up, it is lower than it was previously)
3) Over the course of about 4 hours, the cycle repeats and the pressure drops to below 1 bar and the boiler will not fire up again.
4) I have to pressurize manually to 1.5 and reset the boiler. Then we repeat the cycle with me having to climb up into my loft every 4 hours.

I have tried pressurizing it all the way to 2.0 bars and that doesn't help. Buys me a bit more time between having to reset it that's about it.

I have a video of it but as a new user I am not allowed to provide direct links. Here it is:
youtube.com/watch?v=z_YZZ6fAfcw

This is after I pressurized it 2.0. It comes back to 1.98 or so. But you can see that after several cycles it will drop to below 1. What could this be? It doesn't feel like a leak since it's not a gradual drop. It is a sudden drop every time the boiler kicks in.

Any help will be appreciated very much.

nickcc

The pressure relief valve could be passing. I have the Viessman 100 which is 3 1/2 years old, the boiler failed to ignite just over 3 years ago so we contacted the installer, he advised me to contact Viessman and try and get them to repair foc as just outside guarantee, turned out that there was a 5 year parts and labour guarantee so boiler repaired foc. I mention this as most purchasers and some installers believe there is only a 3 year guarantee even on the later Viessman boilers.

macman

PRV, EV, or a leak on the CH circuit. Check and eliminate in that order. The first two are easy, the latter could be on a concealed run of pipework.

bassamnz

Thanks. I called Viessman and they are sending a guy over. My installer says this is a PRV issue.

The boiler will not fire anymore unless I put it into service mode. But no fault code. Weird huh.

J_B

So, just curious but what do PVR and EV stand for??

macman

Is the PRV lifting? Tie a small bag on it and it will be obvious if it is. If so it will probably need replacement, as they rarely reseat fully.
Expansion Vessel. Pressure Relief Valve.