Boiler pressure not dropping back to 1.2bar

[pinheadplanet]

Hi

Problem I'm having at the moment is that the boiler pressure only returns to 1.5 bar when cool. I released some pressure in the system by opening the bleed valve on a rad so it went back down to 1.3 bar but still now only returns to 1.5 bar after the heating has been on.

Before all this happened I recently repressurised the Expansion Vessel (previous post), doing it the proper way, draing the water out of the system and pumping the water out of the EV, repressurising it to the correct value just to realise that it was the valve that was leaking causing my initial problem, so I replaced the valve.

Everything was fine for a week and the pressures were constantly correct but then to add inhibitor I isolated the bathroom rad, bled the pressure and chucked in a new dose of inhibitor, opened the rad valves again and repressurised the boiler a little, back to 1.3 bar, only since this is it not reurning to 1.3 bar when cool.

What's going on?
Thanks

 

[Mottie]

When you say cool, how cool do you mean? I have to leave mine off a good few hours for it to be truly cool.

 

[pinheadplanet]

When you say cool, how cool do you mean? I have to leave mine off a good few hours for it to be truly cool.

Yeah, hours! It's off for 4 hours in the morning, plenty of time to return its 'normal' cool temperature/pressure

 

[terryplumb]

What does the pressure rise to when heating has been on for an hour ?

 

[pinheadplanet]

It's currently on 2.0/2.05 at the moment and it's been on for half hour. Don't think it goies much higher, maybe 2.1bar before the heating cuts out as per (I guess) the rad thermostats

 

[Madrab]

How large is the system, how many rads? If you tap the gauge, does it drop then?

 

[pinheadplanet]

How large is the system, how many rads? If you tap the gauge, does it drop then?

8 rads. Under the capacity of the boiler. Tried tapping the gauge as someone said these are cheap parts but this didn't do anything

 

[pinheadplanet]

Yeap, definitely only going up to just 2.0 bar when hot

 

[Harry Bloomfield]

If just left for a long period, does the water pressure gradually increase generally?

 

[pinheadplanet]

If just left for a long period, does the water pressure gradually increase generally?

No it doesn't, I don't think the inlet is valve is partially open.

 

[Madrab]

8 rads. Under the capacity of the boiler

Nothing to do with capacity .... have you checked the EV again? With only 8 rads, over a half a bar rise is quite a lot unless all the rads are quite large.

When filling the gauge may not be rising correctly too so you may have actually raised it 1.5 not 1.3 and the gauge wasn't registering properly.

If it settles down to regular pressure swings and stays at that then I wouldn't worry too much.

 

[pinheadplanet]

When filling the gauge may not be rising correctly too so you may have actually raised it 1.5 not 1.3 and the gauge wasn't registering properly.

I already released some water from a rad, taking the pressure when cold back down to 1.3 but it's still returning to 1.5. Might have to drain and check the EV again, as you say.

 

[Madrab]

Check the pre-charge pressure too, what are you pressurising the EV too and what boiler is it?

 

[pinheadplanet]

Check the pre-charge pressure too, what are you pressurising the EV too and what boiler is it?

When you say Pre charge pressure what's that, the pressure it's at now when cold? I pumped all the water out of the Ev and then pumped it to 0.8bar if I remember correctly. It a Halstead Ace High boiler

 

[Madrab]

The pre-charge is the pressure that the EV is charged to when the system is depressurised and the EV is emptied of water, as you have mentioned.
If the EV was full over water before, as the vessel wasn't holding pressure, I'd redo the pressurising exercise again just to be sure. Depressurise the system, leave a wet CH connection open whilst checking, pressuirising and then re-check the pressure again. 0.8 should be fine.