Vaillant boiler pressure range

[gtpassay]

Hi, I have a unvented system. When my boiler is cool (23 'C degrees) the pressure goes down to 1 bar (sometimes 0.9 bar), when heating and hot water are on, the boiler pressure can go up to 2.4 bar. Is this normal? I have had low pressure issues before and had the heat exchanger changed but not sure what I am seeing now is a problem. Thanks

 

[oldbuffer]

1. I'd get the expansion vessel checked. May have lost some or all of its air side charge.
2. Its quite a large pressure increase between cold and hot. At 3 bar, the pressure relief valve (PRV) is likely to operate and spill water to outside. Once they have operated, PRVs tend to weep.
3. How many radiators do you have?

 

[gtpassay]

I have 10 radiatiors and a megaflo tank. The guy who installed the system said he used more underfloor pipes than he would normally due to delays from the builder. The engineer on my service contract had a look for leaks as I was topping up every 2 weeks when seeing the pressure dropping and he found no leaks anywhere (he previously added a leak sealer). He changed the heat exchanger to eliminate the possibility of a boiler leak 3 weeks ago. I have been checking pressure readings daily since then when the boiler is cool and hot and noticed the large pressure range. Thanks for the advice!

 

[ianmcd]

you need someone to calculate your water volume , you may need a larger expansion vessel, or the existing one is under charged