Boiler pressure dropping when heating is on

[boilerproblems]

Hi all,

First time poster, long time reader, so please go easy on me!

I have a Vaillant ecoTec plus 831 boiler, just over 3 years old now. The problem I have is that when we use the heating, the boiler pressure drops - and the amount it drops is proportional to how long the boiler is on - the longer the heating is on, the more it drops. So it drops from 1.1bar to 0.6bar in about 4-5 days when the heating is on about 6-8 hours a day.

It stands to reason there is a leak somewhere. But I noticed that if the heating isn't on and we just use the hot water, then there isn't a drop in pressure (or if there is, it isn't noticeable).

So it is either a leak in the system, which gets worse when the hot water is pumped through, or there is an issue with the boiler such that when the heating is on, the pressure reduces?

I checked the boiler overflow pipe when the heating was on but didn't detect any moisture in the pipe.

What do people think? Leak in the system that gets worse with hot water, or boiler issue? If it is a leak in the system, I am surprised that it gets worse when there is hot water in it, as I though that for any joins etc, hot water would "seal" weeps shut due to expansion of the copper pipe.

Cheers!

 

[HITGAS]

You need to have the boiler and system checked.

A good service and check over the system should show up what is wronge. Things to check: Expansion Vessel, Pressure relief valve, Heat exchanger, System for leaks.