Nightmare airlocks on open vent heating system

[Jon c]

Hi all,

Got a nightmare situation with a central heating system I recently adopted. It's an open vent S plan system with a combined F&E pipe, with a Worcester greenstar danesmoor 18/25 oil boiler. Covers 10 radiators mostly large double panels, some towel rails and smaller rads too, as well as an indirect gravity fed HW cylinder. 2 rads upstairs the other 8 downstairs. F&E tank is in upstairs attic above highest rad. Some 10mm microbore branches, the rest is 15mm branches from a central-ish point. It's never worked right since day 1, lots of gurgling in pipes and boiler would often cut out/lock out due to air inside it so clearly the system had air in it. Anyway the time has come to sort it out, long story short the system was recently drained down about halfway ie. Upstairs rads and underfloor piping only was drained plus one downstairs rad.

Upon trying to refill, no water came through from the F&E tank. Removed top plug in the towel rad and tried using a wet vac to suck water through - no luck. Tried using and pulsing the CH pump to suck water through, nothing. Eventually managed to refill the upstairs rads by shooting mains pressure water into the system through the drain off, however there's still airlocks in some piping as we can hear it and the boiler keeps cutting out due to air inside it. All the rads in the house bleed water not air, so they appear full. Pump (DAB evosta 3) does run but at only 4-8W when set to maximum speed (it self regulates) and it sometimes shuts off with error code 'running dry'. Spent literally all day playing with mains water pressure, sucking, pulsing the pump, draining more water through the system etc. Whatever air locks exist they will not go.

F&E combined pipe is definitely not blocked, it connects to the system just before the pump so the pump should be pulling water through, but isn't. CH and HW valves been on fill/vent/open setting throughout. We can also see and hear air bubbles going up through the pipe into the f&e tank so it appears to function like it should. Pump assumed to be operating correctly as it was replaced recently since the old one was knackered.

Would really appreciate any advice, I'm slightly losing my mind over this as I can't see any logical reason why the airlocks can't be removed or even found especially since all the rads are full of water!

Thanks, and sorry for the long post, but hope it explains the system reasonably well.

 

[terryplumb]

Have you bled the hot water cylinders coil ?
If you have a magnet ,run it up/ down the feed pipe from the f&E tank. If it's blocked the magnet will be attracted to the pipe.
Have you bled the pump ?
Is there an air seperator ,close to the pump / cold feed ?

 

[Jon c]

Have you bled the hot water cylinders coil ?
If you have a magnet ,run it up/ down the feed pipe from the f&E tank. If it's blocked the magnet will be attracted to the pipe.
Have you bled the pump ?
Is there an air seperator ,close to the pump / cold feed ?

Cylinder coil - yes, there is a manual air vent connected at the top of the coil, just bleeds water no air. Its the only air vent around tho, perhaps some AAVs would help?

Magnet - I know the F&E pipe isn't blocked as I've seen the tank empty rapidly with the main draincock open, but good shout I'll check other points like motorised valves etc. That would certainly explain why rads were impossible to fill without mains pressure!

Pump - have tried to bleed it, neither air nor water comes out, well apart from the occasional dribble even with the screw fully out, think it may be some kind of inbuilt aav but not convinced it's working right.

No air seperator

 

[terryplumb]

Show us pics of pipework, cold feed ,around pump too.
If no water is coming out the pump ,that's sure sign of blocked feed to it.
Is pump actually spinning ?
You told us no water ran out of the f&e when you tried to re fill, and later told us it drained quickly ??

 

[Jon c]

Show us pics of pipework, cold feed ,around pump too.
If no water is coming out the pump ,that's sure sign of blocked feed to it.
Is pump actually spinning ?
You told us no water ran out of the f&e when you tried to re fill, and later told us it drained quickly ??

Will get pics tomorrow, btw the plumbing in general is an absolute mess and will be completely renewed in some years. However think it is 'correct'
Will try and check for blockages tomorrow as well, the pump impellor manually spins easily and also spins electrically (can hear and feel it) it's only a few months old so should be OK!

So no water ran out of the tank when attempting to bleed and fill the upstairs radiators - opened the bleed screw completely and nothing happened. Even took the whole threaded plug out, nothing. But water does run out just fine with the downstairs drain cock open. I assumed this was due to airlocks in the pipework to said rads, not sure if that is correct tho!

 

[terryplumb]

When central heating was in use previously,did all radiators heat up ok ?

 

[Jon c]

When central heating was in use previously,did all radiators heat up ok ?

It's been temperamental from day 1 since I've owned it, there was usually 1 rad (it varied between a couple of them) that wouldn't get warm, but sometimes they all would. We knew there was air problems due to constant gurgling in pipes and often the boiler would lock out due to air. Sometimes the boiler would lock out starting from completely cold as air was stuck in it i.e. nothing got warm. So never worked right although now its worse, whoever last worked on it clearly didn't fill it correctly and now same issue again.

 

[ianmcd]

when draining and filling a system you have to latch the zone valves in the manual position, that is what that lever is for

 

[dilalio]

If you know its air then you'll have to cut some aavs or manual vents in at appropriate points on flow and return above boiler would be a good start.

 

[Jon c]

when draining and filling a system you have to latch the zone valves in the manual position, that is what that lever is for

Cheers, I had done that so in theory water should have been able to flow around the system

 

[Jon c]

If you know its air then you'll have to cut some aavs or manual vents in at appropriate points on flow and return above boiler would be a good start.

Sounds like a sensible plan was thinking a little distance after the pump and before the zone valves might be appropriate for one. Second one perhaps on the return but before or after the bypass valve connection point?

 

[dilalio]

Sounds like a sensible plan was thinking a little distance after the pump and before the zone valves might be appropriate for one. Second one perhaps on the return but before or after the bypass valve connection point?

Wherever you can get them... Start with easiest locations first and see what results you get.

 

[dilalio]

Wherever you can get them... Start with easiest locations first and see what results you get.

Wherever you think pipework goes up, over and down and you can get one on the top of the arch!

 

[Jon c]

Just an update, managed to finally get it working today, installed 2 AAVs on pipework where it looked like air could collect, there is also a manual bleed valve as well nearby. Still no luck with filling the system conventionally via the F&E tank, so again I back fed mains water through the draincock and managed to fill it up this time. Some purging with the pump seemed to help push all the air through and out of the AAVs, heard plenty of hissing! There is still a bit of air in the system by the sounds of it occasional gurgling etc but hoping it will find its way out of the AAVs.

Based on this does it sound sensible to convert the system to a sealed system at some point in the future? The boiler is actually suitable already...

 

[Jon c]

Red circles show my new AAVs and the manual air vent. The higher AAV is on a high point return leg that covers all the rads but not the cylinder. The lower AAV is on a high point flow on a flow leg covering 4 rads, was hoping there would be enough flow through these to look after any stuck air. As you can see the plumbing generally is an absolute pile of **** some day it will hopefully all be redone. Combined F&E pipe is just out of shot to the left in the flow pipe leading to the pump.