Grant Combi 90 - loses pressure

[Marnhullman]

I have a Grant 90 boiler that should be at 1 bar pressure when cold but it keeps losing pressure to zero bar.

I have replaced the pressure vessel and the pressure relief valve but it still keeps losing pressure however this doesn't cause it to malfunction or cut out except that the domestic hot water pressure is low.

The boiler is located in a holiday home that is only used at the weekends and I thought this could be the problem but although I top the system up when we arrive on a Friday night to 1 bar it frequently drops to zero over the weekend so I think this is a red herring.

I'm told the only way the system will lose pressure is if there is a leak - a hot tap drips occasionally if it isn't turned off properly - but I can't find any actual leaks.

I'm concerned that I am repeatedly topping up the system and diluting the rust inhibitor - assuming there is any left after the number of times I've done this.

If the heat exchanger was furred up could this cause the problem?

Grateful for any clues/advice.

Mike Collard

 

[Gees]

You have a leak... It may be only a drip but its only got to be a tiny drip to take the pressure down to nothing over a period of time.