20 Jan 2016
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United Kingdom
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 (Pre determined cut off point) 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 here.

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.
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It was serviced in November. This started in December, on and off. Since we got back from holiday it has gotten worse.

The boiler is now 1.5 Years old. It is under warranty and one of their guys is coming to check it out but I want to be able to tell him what is happening.

The guy who is also coming said that it cannot be a pressure problem because Viessman does not have a pressure sensor. I can't fathom that this is true but we will see.

The Boiler will not fire and there are no error codes. The only way it will work is by putting it into service mode.

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