Ferroli modena pressure

[laurelandhardyconstructio]

Hi everyone,

I have noticed my central heating pressure gauge rising upto just under 3 bar recently,the central heating stat on the front panel is set to just over 60.

But when i turn this down to just over 50 the central heating pressure gauge drops down to 2 bar.

I had someone out last year to pump up the expansion tank and wondering if could be the cause?

 

[Terry7556]

possibly read the sticky at the top of the index page on boilers/ central heating.find the section on recharging your expansion vessel

 

[MANDATE]

I think the boiler stat settings have very little to do with your problem.
The water pressure when the heating is off is normally around 1bar (or should be). It then depends on the volume of water in the system.
With the heating on temperature rises and the water expands.
The extra water has to be accommodated by going into the expansion vessel (providing there is room for it).
This compresses the 'air' in the vessel and both the air pressure and water pressure rises.
If the vessel is the correctly rated to deal with the system volume the pressure rise will be around 1 to 1.5bar.
So starting with 1bar and rising to 2bar or 1.5 rising to 2.5 is about the norm.
Now when the system goes off due to room stat or boiler stat the pressure will drop back to the 1bar until the heating switches on again.
The pressure relief valve opens at 3bar so quite rightly you dont want to be approaching to close.
You did not say what the starting pressure was, but you could consider reducing it slightly so the max pressure would also be reduced.
The vessel is somewhat like a car tyre and may lose a little air over time.
The vessel has a diaphragm and the vessel is charged with air before any water is introduced. This gives the maximum of vessel volume of air to compress.
If the vessel was not charged or undercharged there would no air or a reduced amount of air to compress.
Its well known that half the volume will double the pressure so as the pressure rises higher than intended the PRV prevents any serious problems.
Any attempts to recharge the vessel must have the water pressure removed and allow the water inside the vessel to escape to atmosphere.

Also the vessel is normally connected to the system with a flexible pipe and these pipes can get blocked or partially blocked. This means the vessel is prevented from doing its job correctly.
If the diaphragm in the vessel is 'holed' or ruptured then again it can't function.