Condensing boiler losing pressure

[chumley0312]

We have a Condensing boiler, fitted approx. 3yrs ago. Over the past couple of weeks it appears to be losing pressure slowly, around .3-.5bar over a 2 week period, which was noticed 2 weeks ago as the boiler failed to light for hot water. I refilled the boiler to 1.5bar, and bled all the rads, a bit of air came out of 2 of them. Checked a couple of days ago, and its just over 1 bar. I have been all over the house, and cannot find any leaks or weaping joints anywhere. When fitted, new tails and TRVs were fitted to all rads bar 1, where just new tails were fitted. (Rads are all around 20yrs old, apart from the bathroom towel rad). It was fine, and never had to fill up until this issue.
We have had a conservatory built, and an extra radiator added to the system, but I have checked the connections to the pipework thoroughly, and nothing seems amiss. I am going to call out the guy that fitted the extra rad, as it seems too much of a coincidence, but wondered if there was anything simple I have missed. The PRV outside does not appear to have leaked.

 

[sooey]

You'll get different readings according to whether the system's hot or cold, or even if the pump is running or not in some cases.
So to check it accurately you need the system off and cold.

 

[chumley0312]

Thanks

I have always checked it cold, when nothings been running for a while. The pressure raises normally when in use.

 

[chumley0312]

OK. Last night, I filled the boiler to 1.5bar. The system was cold.
Switched it off, so nothing would kick in.
Checked this morning, and was sat at 1.1 bar.

Should I be concerned about this??

Thanks

 

[Justin Passing]

Suspicious, but leave it for longer to be sure. Fresh water has air in it which comes out, especially when heated, and is released from the automatic air vent. That drops the pressure, after which it should be steady.

 

[ALCPlumbing]

Check it when it's hot and also check the pressure relief pipe that should poke out of the wall behind the boiler. I suspect you may have expansion vessel problems. If that is the case and you're lucky it may only need recharging. Have a look and post the results of your findings.