Gurgling and air in central heating

[John.g]

Yes, maybe through the leaking NRV but very unlikely.

The most likely place for air ingress one might think would be at at attic rads even though these should still have ample positive pressure even if boiler pressure was =<1.5bar.
If you vent them with pump running does water definitely flow out after a burst of air? and does the same apply to all the other rads?

 

[jim843]

Yes, maybe through the leaking NRV but very unlikely.

The most likely place for air ingress one might think would be at at attic rads even though these should still have ample positive pressure even if boiler pressure was =<1.5bar.
If you vent them with pump running does water definitely flow out after a burst of air? and does the same apply to all the other rads?

The attic rads never have any air in them. They only had air in them before the bathroom was fitted. After the bathroom was fitted, air appeared in the bathroom towel rail instead.

I can always cap off the upstairs rads on the second floor and run the system for a bit to see if the air stops?

If the attic rads are pulling in air, why would it end up one floor down?

 

[John.g]

Its a mystery to me why any air is getting in!, does the towel rad vent water??.

 

[jim843]

Its a mystery to me why any air is getting in!, does the towel rad vent water??.

Yep, it vents water.

There’s some air. Then water.

I can repeat this every day.

 

[jim843]

Its a mystery to me why any air is getting in!, does the towel rad vent water??.

I re-read your previous comment: did you say vent with the pump running? I always vent when the pump is off.

Also, air only appears in the towel rail when the heating system has been on. In summer there’s no air in the towel rail. This might be expected, I don’t know.

 

[John.g]

No, vent with pump off but when water is circulating in any pressurized/sealed system then there should always be water pressure at the vent when opened, if no water then ensure that air is actually venting and not being drawn in.

I have two rads in a upstairs attic conversion that always run with a slight vacuum (open vented system) but it has never caused any problems because there are no leaks anywhere associated with them.

 

[jim843]

No, vent with pump off but when water is circulating in any pressurized/sealed system then there should always be water pressure at the vent when opened, if no water then ensure that air is actually venting and not being drawn in.

I have two rads in a upstairs attic conversion that always run with a slight vacuum (open vented system) but it has never caused any problems because there are no leaks anywhere associated with them.

There’s always pressure. The air is always forced out and I get water.

 

[John.g]

OK, Thanks, stumped for sure, can you please post the exact model of the Baxi Combi you have.

Also, what is boiler flow temperature on CH.

 

[jim843]

OK, Thanks, stumped for sure, can you please post the exact model of the Baxi Combi you have.

Also, what is boiler flow temperature on CH.

Sure, it’s a Baxi Duo-tec Combi 33.

I think it’s anything from about 60 to 80. Will look more closely.

 

[John.g]

At least one small query is answered in the schematic, the E.Vessel is on the flow side, the reason why the pump pressure drops on start up.