Repeated airlocks in central heating system

[gas112]

18 rads do you have an additional expansion vessel on the system other than the one inside the boiler . You maybe losing water out of the prv thus why you have to bleed rads to fill it back up . 18 cast iron rads is a lot of expansion when hot.

edit
never seen gasguru earlier reply

 

[gaj2002]

Ok great, I can check what was done, although if Ideal require a chemical flush then I reckon they would have done that to comply with the warranty conditions.

I’m sure I can get a magnetic filter fitted, perhaps by other engineers. But would that be causing this problem? I’m sure you’re right it needs to be done though.

Perhaps a bit of a random suggestion but the utility room rad has the TRV on the wrong side (return rather than flow). It seems to be slow to warm up so it might be the case that it’s not bi-directional. It’s a Boss TRV from presumably 2007 as that is when the previous owner did their works. Could that be sucking air in and causing the problem?

Thanks
Gavin

Sorry I should update this to say I checked and there was indeed a magnetic filter.

The installer is coming on Friday, he says it is likely the system just needs balancing, although I also plan to get him to empty the magnetic filter.

Anything else I should ask him while he is here?

 

[gaj2002]

Corrosion in your system MAY be the cause of the persistent problem with gas build up ,if indeed that's what it is. If the system is sucking in air ,it won't have anything to do with a TRV, (which should have arrows raised embossed on its body to show direction / bidirection)
The omission of a magnetic filter ,which I find hard to believe has not been fitted, would not in itself cause your issues ,but may be a contributing factor.

Thanks Terry, there is indeed the magnetic filter, we are ok on that one.

 

[gaj2002]

Has the system got an additional expansion vessel (red coloured) as the boilers vessel will be undersized to cope with the no. of rads and the higher volume of cast iron rads.
If there's no additional vessel you should check the boiler safety valve for drips and if this is the case it could be a source of air ingress.

Sorry slow reply, I didn't get the notification about this message

Ok I don't think we have an expansion vessel, I'll check with the installer when he comes on Friday

How would I identify the boiler safety valve?

 

[gaj2002]

If you have eighteen cast iron radiators I suspect the water volume is very high. You need lots of inhibitor. We have steel column radiators and have a similar situation. We had seven (big ones) removed for decorating. When they were refitted and the system refilled we were getting gas in the system that would come back after a few days after being bled. Its taken about 3.5 litres of MC1 to restore everything back to normal. A magnetic filter is a great way to dose the system with inhibitor as well as its other benefits.

Also gasguru is correct - the water volume needs a bigger expansion vessel.

Sorry slow reply, didn't get the notification about this message, but anyway thanks, I did raise the question about quantity of inhibitor on the phone but he was pretty confident it was just the balancing that was needed... I'll probably let him try the balancing on Friday and see if the problem recurs again. However I'll also ask the question about the expansion vessel. Would it also be a good idea to call Ideal technical support about the expansion vessel issue? I don't want a warranty problem down the road and also the installer can't really argue with me if I say Ideal have said the installation wouldn't be adequate and they wouldn't honour the warranty

EDIT - it's five cast iron radiators out of a total of eighteen... sorry if this wasn't clear, I wouldn't have been aware of what an important detail this was. Would you still say we need the expansion vessel? I've just checked and it doesn't look like there is one there

 

[gaj2002]

Isn't there just a simple explanation that with such a large system that was completely emptied it's just going to take a while to get all the air out?

sorry slow reply, didn't get the notification about this message

Yes, I've been through about eight two-week cycles of force out upstairs airlocks by turning off downstairs rads, bleed to remove air, system fine for a week, then start losing loft rads, then lose one first floor rad, then repeat

I think after eight goes, I'm reasonably confident it's not just the initial air from the building works now

However please say if anyone with more (any) experience than me disagrees?

 

[gaj2002]

18 rads do you have an additional expansion vessel on the system other than the one inside the boiler . You maybe losing water out of the prv thus why you have to bleed rads to fill it back up . 18 cast iron rads is a lot of expansion when hot.

edit
never seen gasguru earlier reply

Hi, sorry slow reply, didn't get the notification about your message

thanks for replying, it's only five cast iron out of eighteen total, would you still say we need an expansion vessel? I've just looked and i can't see one on the installation

 

[Gasguru]

Take a look at the installation manual but the safety valve is a 15mm pipe that usually terminates on the outside of an external wall.

 

[gaj2002]

Update on this - installer agrees we likely need an expansion vessel, he's going to come back and fit one