Pressure guage on sealed heating system

[wedge69]

Hello,

We have a heat only boiler that provides central heating and also heats the water in the unvented cylinder.

Tge pressure gauge in the airing cupboard has a red line marker at 1.5 bar. Is this the maximum recommended pressure when the system is hot or cold? I have no idea what temperate our system is supposed to be filled too, but it currently operates fine at 0.8 bar cold, 1.3 bar hot.

Thanks

 

[TCCHeating]

Depends on position of boiler (vertical height) relative to where the pressure guage. But generally the pressure should be set between 1 and 1.5 bar when the system is cold. 0.8 seems a little low but nothing to really worry about! Put it up to 1 bar and you should be fine.

Only start worrying if the pressure drops regualarly and you are topping the system up regularly

Ps. That red line marker is adjustable. So just ignore it!

 

[wedge69]

I upped the cold pressure to 1.0, but when hot the system still isn't much above 1.3. Is that an issue, or expected because of the expansion vessel or some such other feature.

The pressure gauge and the expension vessel are both up in the airing cupboard (boiler is downstairs) and are at the end of a meter and a half long pipe teed off the central heating.

 

[MANDATE]

Thats OK! The rise is due to the fact water expands when heated and the extra water goes into the expansion vessel and compresses the air, so both air pressure and water pressure rise.
The amount by which it rises depends on (a) volume of water in system (b) the temperature of the heated water (c) the capacity of the expansion vessel and the pre charge pressure of the expansion vessel.
A rise of only 0.3 bar is good.
Time for concern is when the heated pressure gets over 2.5 bar knowing the pressure relief valve is set to operate at 3.0bar

 

[wedge69]

Thanks for the response.

Cold pressure seems to haveg dropped to 0.9 when cold now, but hot is still 1.3. All radiators are roasting hot and I don't think there is any air in the system, so is this just the system settling down to its working pressure?

I find it quite hard to get an accurate cold reading - if I check at the same time on different days I get variations of 0.1 bar. I guess I am worrying about nothing unless the pressure drops right to zero?

 

[twgas]

It sounds fine to me, stop worrying about it.