Another noisy combi boiler

[lizzy]

I've recently drained our central heating system to move a radiator. It's a Vokera combi boiler. I moved the radiator and re-filled the system as normal. Now when the heating starts or the hot water comes on, the boiler makes a short banging/gurgling noise and then runs as normal. The temp gauge reading is also much higher (when the system isn't running). The noise sounds like air trapped in the boiler. But I've drained the system many times before and never had the same problem. There is a screw at the top of the boiler that says 'Air'. Does the problem sound like air trapped? If so, do I just bleed the screw like you bleed the radiators?

Thanks in advance.

 

[ChrisR]

Does the problem sound like air trapped? If so, do I just bleed the screw like you bleed the radiators?

Thanks in advance.

Yes,
and you leave that air vent cap loose. Inside there's float which rises to seal the exit if water's present. Air bypases the float to exit. SOmetimes they weep slightly.

 

[lizzy]

Thanks Chris.

I had a look last night, and what I thought was the vent on the bolier wasn't (or at least nothing happened when I undid the nut). Where is the vent likely to be? The boiler is a Vokera Excell 80SP if you know it at all.

 

[ChrisR]

Can't remember! BUt the thing you're after looks like a car tyre valve cap. If nowt comes out it's either let all its air out already or is full of scale. If you're in Scotland (Vok land) you'll have soft water so it won't be that.

 

[lizzy]

Ahh, I've seen that and I did let a bit of air out, but I didn't want to carry on as it seemed like there was a lot. So I dug out the installation manual it said this valve was for charging the 'expansion vessel' to 1 bar with a 'foot pump or equivavlent'. So I assumed that this was meant to be full of air and left it alone. Do I need to let the air out of here then? As I was flicking through the manual I noticed that the pump has an 'automatic air release', does this release air from the pump?

 

[leafy]

Don't let any more air out from the expansion vessel - it's supposed to be in there.

I'm pretty sure the automatic air release is mounted on the base of the pump and should have been opened when the boiler was initially filled. If not, 1 turn anti-clockwise will do it.

Also look for manual air release points in the heating system pipework.

 

[croydoncorgi]

If you've vented the 'pre-charge pressure' in the expansion vessel (by letting air out of a 'car tyre type' valve) then there's no point messing about any more trying to get air out of the rest of the system. You must first get the pre-charge pressure back to what it should be and that requires letting water out the system (again!) until the pressure on the gauge is zero, then pumping more AIR into the expansion vessel up to the right pre-charge (usually 0.5 Bar but it does vary) measured at the valve NOT on the main pressure gauge. Only then can you re-fill the rest of the system until pressure is 1 Bar, and re-commence getting air out of the boiler, plumbing and rads.

Unless you follow this procedure, chances are the expansion vessel will 'lock up' when the system is at the correct pressure. When water heats up it expands and there'll be no room for expansion. The pressure will rise and the Pressure Relief Valve will lift, releasing water down your outside wall. Then your PRV will continue to leak, giving more problems with pressure control into the future....

Best idea might be 'call an engineer'.....

 

[lizzy]

Ok, cheers fella's. I only let a little air out of the expansion vessel, as I had a feeling something wasn't right. We tend to run the heating at the lower end of the pressure gauge anyway so we will probably be alright. I'll have another look for some vents. But it wouldn't hurt to have the boiler looked at, it could do with a service anyway.