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Mar 12, 2020
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General Plumber
Ok I have a dual oil and back boiler system. Ever since I moved into this house of horrors I’ve had no heating upstairs. Downstairs rads ok but nothing upstairs . No air in system and all valves open. Can’t figure out why no pressure upstairs. Had the whole system professionally flushed as well and both circulating pumps working 100%. Any help much appreciated
 
By no pressure I mean when I have heating on and open a radiator to bleed very low presssure obviously forcing any water out. No idea what or were a zone valve is.
 
This is a zone valve, although some have plastic heads. Usually located in cylinder cupboard. Have you tried closing all rads downstairs?
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Yes I have a zone valve. When oil heating is on its moving automatically to open position. I have tried closing all down stairs rads but no joy. I have noticed that when oil heating on it still heats water in my back boiler of open fire
 
Ok. Possible but not definite the ball valve in the loft is stuck and you don't have enough water in the system. Check the small head tank in the loft and see if there's water in it. At least rule this out first.
 
Ok. The system is full, bled, pumps ok and all valves open or operate. This has been a continuous problem since you moved in you say?
Any chance you could give a rough sketch of system layout? It's possible and again not certain it's piped wrong and there's a dead short through your back boiler, preventing flow around some of the heating circuit.
 
Ok. The system is full, bled, pumps ok and all valves open or operate. This has been a continuous problem since you moved in you say?
Any chance you could give a rough sketch of system layout? It's possible and again not certain it's piped wrong and there's a dead short through your back boiler, preventing flow around some of the heating circuit.
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Where does the top arrow go to and where is the bottom arrow from?
 

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Where does the top arrow go to and where is the bottom arrow from?
Top pipe goes onto bottom side of cistern and bottom pipe is the feed for upstairs heating. The pump in picture is the pump for back boiler. It gets warm when oil heating on as water flows thru it in to back boiler which shouldn’t happen
 
Installing a NRV (non return valve) between the back boiler pump and tee piece would hopefully solve your problem.
Water takes the path of least resistance, I'm pretty confident the loop back through the back boiler offers less resistance than your upstairs heating run and therefore you have a dead short bypassing it.
I will point out though that Is not a proper way to intertwine two heat sources. I know you inherited the problem but it really should of been thought out properly.
 
Installing a NRV (non return valve) between the back boiler pump and tee piece would hopefully solve your problem.
Water takes the path of least resistance, I'm pretty confident the loop back through the back boiler offers less resistance than your upstairs heating run and therefore you have a dead short bypassing it.
I will point out though that Is not a proper way to intertwine two heat sources. I know you inherited the problem but it really should of been thought out properly.
Wouldn’t even know where to begin to solve the issue correctly although I will put a NRV in place
 
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Wouldn’t even know where to begin to solve the issue correctly although I will put a NRV in place

The system can work fine and safely as it is but there are better ways to involve two heat sources in the same system. The valve after the pump and before the tee could even be an NRV and if so I would say its failed if it is.
When replacing take note if the direction of flow arrow on the new valve, it needs to allow flow away from pump and prevent it coming the other way.
I hope this will solve your problem and I suspect it will. The vents for back boiler and boiler aren't compromised are they? By that I mean before the pumps on the back boiler and boiler flows and not elsewhere?
 
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It sounds to me if you have an old back boiler which heats your hot water you may have a stuck none return valve it looks like a compression socket but longer.
 
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Installing a NRV (non return valve) between the back boiler pump and tee piece would hopefully solve your problem.
Water takes the path of least resistance, I'm pretty confident the loop back through the back boiler offers less resistance than your upstairs heating run and therefore you have a dead short bypassing it.
I will point out though that Is not a proper way to intertwine two heat sources. I know you inherited the problem but it really should of been thought out properly.

There’s already one installed right hand of the pump by the looks it’s either installed the wrong way or the pump and zone valve are on the return
 
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It hard to see from your pictures how and where the pipes go but I see at least one non return valve there could be another ? these can become stuck or blocked with debris I think you will need a engineer who understands combined heating systems to diagnose and solve your problem. Kop
 

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