Pressure problems on closed heating system

[maxwe789]

I have an old radiant boiler which when running would get up to 3 bar. This would activate the pressure release out the back of the house resulting in too low pressure when cold.

I have had problems with the pressure vessel before so I though it might need pressurising again so I:

Drained the system
pumped up the vessel to 1 bar
re-filled the system with inhibitor
bled all the raidiators

Still no luck though? Any Ideas?

Many thanks

 

[WHPES]

leaking prv?

 

[Alpha man]

Does the expansion vessel loose its air?

 

[maxwe789]

It seems to lose air over a year or two. The pressure release valve seems a little sensitive and starts leaking at about 2.7 bar as indicated on the dial.

I have just cooled off the central heating and the pressure has dropped to about 2.1 which is higher than I was expecting. My boiler doesn't seem to kick in until it has at least 1.5 bar of pressure whereas the manual says it should operate from 0.5 to 2.5.

How much should the pressure move when the system is on? I wonder if the pressure switch is too high and the prv is too low so the system doesn't have enough range to run in??

 

[Reg Man]

Whe many rads on the system? If your volume of water is to much then you may require a larger or additional expansion vessel. Your system pressure should'nt be going up and down that much, thats what the vessel is therefore.

 

[maxwe789]

It's a small mid terrace with 5 rads. Just dropped the system pressure to just above 1.5 bar before kicking off the boiler. It's currently sat at about 2.2 bar and not leaking. Fingers crossed this will see me through the winter and then time for new boiler me thinks as this one is ancient.

 

[Alpha man]

Try getting the pressure around 1 bar when its cold, should be fine then if the vessel has enough air in it!

 

[maxwe789]

If I go below 1.5 the boiler complains of low pressure and will not start up. I ordered a replacement pressure switch but the part came with instructions which involved rewiring certain bits. Didn't look massively involved but nontheless I don't really fancy busting out the soldering iron and making a mess of it.

 

[Alpha man]

Leave it at 1.5 bar then, saves all the hassle!!

 

[maul]

can you just replace switch and connect the new one to the wires of the old one with a terminal block connector?
1.5 bar is quite a high pressure for it to cut out at imho.
also pressure vessel sounds suspect as its not doing its job correctly as reg man says above its either faulty or undersize.
have you added any rads to the system since it was fitted ?