Boiler pressure too high - and too low!

[Rod4444]

Hi looking for some advice please.

We have a Viessmann VT100-W (WB1C 30kW) boiler. It's about 8 years old. I am now topping up the pressure about twice a week.

I check the pressure first thing in the morning when the system (and me) is cold. Pressure is around 0.7. I top it up using the loop to around 1.1 to 1.2.

After it has been running for a few hours and is hot the pressure is around 2.8 almost in the red! I have checked the house and there is no sign of a leak.

Any idea what could be the cause and fix. My theory is water is escaping as steam.

We had an extension built 8 years ago and were persuaded by the builder to replace the 30 year old boiler which, apart from the sensor that was replaced every few years, never went wrong.

 

[gmartine]

So this boiler has now gone wrong after eight years, was it serviced regularly? If not I'd say that was a fairly decent reliability record and now it's time to get an engineer in. The symptoms point to a fairly common issue but it is not a DIY fix.

 

[Rod4444]

So this boiler has now gone wrong after eight years, was it serviced regularly? If not I'd say that was a fairly decent reliability record and now it's time to get an engineer in. The symptoms point to a fairly common issue but it is not a DIY fix.

Hi engineer is the next step. Its been serviced every summer except for 1 during lockdown. Still be good to know what the problem is.

 

[gmartine]

The pressure fluctuations probably relate to an issue with the expansion vessel.

 

[Rod4444]

thank you engineer coming at the weekend