Pretty sure it’s internal. The engineer took the cover off. There’s nothing outside the boiler as far as I know.
Currently reading:
Gurgling and air in central heating
Discuss Gurgling and air in central heating in the Central Heating Forum area at PlumbersForums.net
Pretty sure it’s internal. The engineer took the cover off. There’s nothing outside the boiler as far as I know.
In the attachment is that a PRV on the filling system??.
It's also possible I suppose but very unlikely as I said above that the pump is pulling in a tiny amount of air through that leaking NRV each time it starts especially if the E.vessel is on the discharge side of the pump, the closer to the boiler the greater the chance, if the boiler is under warranty then that should be covered? its the only part that has direct communication to the atmosphere via the leak even though pressurized.
It's also possible I suppose but very unlikely as I said above that the pump is pulling in a tiny amount of air through that leaking NRV each time it starts especially if the E.vessel is on the discharge side of the pump, the closer to the boiler the greater the chance, if the boiler is under warranty then that should be covered? its the only part that has direct communication to the atmosphere via the leak even though pressurized.
Attachments
Maybe I’m mixing this up: the leak is on the valve that has an arrow on it.
The arrow you have drawn on the photo: do you mean a pressure release valve? I don’t know what that black thing is.
Attachments
Yes, I would replace it as every other possibility seems to have been reasonably exhausted. Maybe its under warranty?.
The valve thats leaking is a non return valve (NRV). the PRV I'm referring to is a pressure reducing valve called a PRV (as is the safety valve also called a PRV, a bit confusing) the pressure reducing valve above is/should be connected dirrectly to the filling hose?.
Forget my reference to that PRV, thats the isolating valve for the filling hose.
The valve thats leaking is a non return valve (NRV). the PRV I'm referring to is a pressure reducing valve called a PRV (as is the safety valve also called a PRV, a bit confusing) the pressure reducing valve above is/should be connected dirrectly to the filling hose?.
Forget my reference to that PRV, thats the isolating valve for the filling hose.
I seem to remember from a couple years back a Baxi engineer saying that this filling loop is old and should have been replaced when the boiler was replaced. Maybe I’m misremembering, though.
You’d think the boiler would be under warranty but the installer has moved and I’ve no idea where they live now. Considering the mess they made - leaking joints under the boiler, not fitting the soak away - I should probably get someone else in.
Ok, I’ll have a look and see what screwfix have tomorrow.
Something like R24 Filling Loop - https://www.NoLinkingToThis/p/r24-filling-loop/83905 with some pipe and compression fittings to connect to that new loop?
Another thought: the isolation valve with the handle before the filling loop would stop the leak, if any, right?
Or are you thinking that the leaking NRV is somehow pulling air into the system even though the filling loop isolation valve is closed?
Last edited:
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 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?
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.
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.
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.
Sure, it’s a Baxi Duo-tec Combi 33.
I think it’s anything from about 60 to 80. Will look more closely.
- Messages
- 2,558
If that schematic is correct then perhaps we have the answer. The pump is pumping towards the point of no pressure change and therefore the system is under negative pressure. Any weak joints will be drawing air in, alternatively the the system being under negative pressure means you will pull any dissolved gases out of solution.
The point of no pressure change is where the EV connects into the system and is the EV pressure itself, with the circ pump off then this pressure will be exactly the same throughout the circuit, after allowing for elevation. With the circ pump running, while the pressure where the EV connects to the system will still be exactly the same then its possible to get negative pressure(s) somewhere but only due to pipe friction losses due to blockages?.
Maybe all combis have their EVs connected in likewise, someone might care to watch their own boiler pressure gauges on start up and note whether it rises or falls with pump start and also its magnitude, the one above certainly moves more than I would have expected, even though theoretically possibly correct, possibly pointing to restriction somewhere?
If the system isn't ingesting air then all this air must be trapped since initial filling but as its being slowly vented then the boiler pressure should gradually fall and require top up but it isn't. Perhaps drain the whole system again and fill very slowly stopping to vent from the bottom up.
The only other thing maybe worth checking out is the PHE, if it had a pinhole maybe possible to keep the system nicely topped up from the mains and if its at or near the system pressure then no problem with boiler PRV lifting. but plenty of oxygenated air gaining access.
Suggest shutting off the mains feed at the boiler and open a hot tap and leave open for a few hours with CH in service and see if any change in behaviour, presume the diverter valve isolates the primary water from the PHE but something may still show up.
A interesting riddle alright.
Maybe all combis have their EVs connected in likewise, someone might care to watch their own boiler pressure gauges on start up and note whether it rises or falls with pump start and also its magnitude, the one above certainly moves more than I would have expected, even though theoretically possibly correct, possibly pointing to restriction somewhere?
If the system isn't ingesting air then all this air must be trapped since initial filling but as its being slowly vented then the boiler pressure should gradually fall and require top up but it isn't. Perhaps drain the whole system again and fill very slowly stopping to vent from the bottom up.
The only other thing maybe worth checking out is the PHE, if it had a pinhole maybe possible to keep the system nicely topped up from the mains and if its at or near the system pressure then no problem with boiler PRV lifting. but plenty of oxygenated air gaining access.
Suggest shutting off the mains feed at the boiler and open a hot tap and leave open for a few hours with CH in service and see if any change in behaviour, presume the diverter valve isolates the primary water from the PHE but something may still show up.
A interesting riddle alright.
Don't see it that way SJB but could be wrong, pages 36/37 of the attached explains even though they use very low pressures to demonstrate how a negative pressure may occur.
- Messages
- 2,558
Yes, so my above comment wasn't worded correctly. The pump will maintain a differential pressure though. Therefore if it's only able to increase pressure slightly on the discharge the rest will be seen as a negative pressure on the suction side.
If I understand: the EV can cause negative pressure in the system. So a weak point/pin hole leak could be anywhere?
Your suggestion is:
- switch off the main feed (the cold water?)
- switch CH to service (not sure how to do this? Just switch to hot water only?)
- Run hot tap in the kitchen for a couple hours
- Watch for pressure drop/change?
@SJB060685 and @John.g...
I'm off next week so will fit an isolation valve to the leaky NRV. I'll also try the steps suggested above.
Sounds like I'm getting closer to the dreaded "replace all the pipework in the house"?
Supposed to be getting carpets fitted in 3 weeks. The last in the house after a 7 year renovation in my spare time. Oh well, better know now before getting the carpet fitters in...
I'm off next week so will fit an isolation valve to the leaky NRV. I'll also try the steps suggested above.
Sounds like I'm getting closer to the dreaded "replace all the pipework in the house"?
Supposed to be getting carpets fitted in 3 weeks. The last in the house after a 7 year renovation in my spare time. Oh well, better know now before getting the carpet fitters in...
I don't think the EV is causing negative pressure Jim.
Re 1 to 4 above .
Shut either valve 13 in schematic post 80, or just shut the main stopcock, either will cut off the cold water supply to the combi side of the boiler, open any hot tap, (hot) water flow should stop.
Ensure boiler on CH say like now, just watch the pressure gauge for few hours for any change.
When complete shut hot tap and restore the cold water.
Just trying to establish if there is a leak between the mains and the boiler "water" via the HW heat exchanger. (PHE).
Ok, gotcha. Thanks.
I can do this tomorrow (probably -- weather dependent!).
Do you want me to run the CH as normal (Tado switches various rooms on/off during the day)?
Reply to Gurgling and air in central heating in the Central Heating Forum area at PlumbersForums.net
