HELP Header Tank not draining

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jorgemandrade

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I have got a typical gravity fed heating system with cold water and small header tanks in the loft, hot water cylinder, heating control, pump and 2-way valve in airing cupboard and back boiler and fire on chimney breast downstairs.

Today I drained the central heating system by removing a radiator downstairs, a lot of water came out. After capping off the pipes to the radiator that was removed I went back to the loft and to my surprise the header tank was still completely full. I don't think the water level moved one bit.

I want o refill the system but I don't know if it will be possible now. Any advice would be much appreciated. Thank you.
 
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Small cistern is known as F&E cistern.
You drain the system via the vent pipe but to refil, it needs to happen via the 15mm pipe.
Most likely there will be a blockage in the tee that connects the 15mm to the cylinder and the system
 
DP said:
Small cistern is known as F&E cistern.
You drain the system via the vent pipe but to refil, it needs to happen via the 15mm pipe.
Most likely there will be a blockage in the tee that connects the 15mm to the cylinder and the system
Click to expand...
That tee is most likely in the ceiling void or in chimney breast where the boiler is which I won't be able to access. The 15mm pipe from F&E cistern comes down through airing cupboard so that tee must be somewhere on ground floor. Is there any way to try to unblock it? Could I try to run the pump to see it dislodges the blockage?
 
No don't run the pump with no water in the system you will probably damage it / burn it out .
The only way to clear a solidly blocked pipe is to cut out the blocked section/ or fitting.
The feed may join into the system near the pump ,show us some pics of pipework
 
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Remamber and take all the water out of the F&E tank before you cut out the blocked Tee, or you will get a little surprise
 
Ours is like that too - and DOES fill OK from the F&E tank as you expected yours would.

Worth checking to see what check/gate valves you have on your system. We have one on the mains cold input to the F&E tank to make it easier to shut off a defective ball valve - and that's pretty standard.

BUT we also have a gate valve in our airing cupboard that shuts off the OUTPUT from the F&E tank in the loft above. This allows our system to be drained down without having to even go up into the loft as the system is open vented. If you find you have such a valve too:

1. It could have been turned off in error at some point
2. It could have been turned off for some reason, and the gate valve stem has snapped with the valve in the closed position (this is the most likely cause of a perceived blockage in my opinion as I've seen gate valves fail like this several times)
3. It could have been turned off deliberately after the system was last filled from the F&E tank

Possibility 3 isn't as daft as it might sound. Water in your F&E tank is essentially stagnant between work being done on the system. On our system, I make sure I pop some extra additive in the tank water after I have completed any work and refilled - but it can still get pretty foul and disgusting in there if it's years down the line when work is next done, to the point you wouldn't want to draw that muck into a microbore system like ours. So, before I do any work on our system, I actually shut off the cold feed into the F&E tank and pump all the filth out, clean the tank out, and then I can be sure I'm drawing clean water in when I actually do any work. A way to be CERTAIN filth can't get inadvertently drawn in, is to shut down the output after a fill (as I would be able to do) - though I always leave mine open as there will be some slight losses through evaporation., bleeding air out etc.
 
Last edited:
jorgemandrade said:
That tee is most likely in the ceiling void or in chimney breast where the boiler is which I won't be able to access. The 15mm pipe from F&E cistern comes down through airing cupboard so that tee must be somewhere on ground floor. Is there any way to try to unblock it? Could I try to run the pump to see it dislodges the blockage?
Click to expand...
page10image1663336768


Look at this diagram, Are you sure the tee is out of sight?
 
terryplumb said:
No don't run the pump with no water in the system you will probably damage it / burn it out .
The only way to clear a solidly blocked pipe is to cut out the blocked section/ or fitting.
The feed may join into the system near the pump ,show us some pics of pipework
Click to expand...
I have attached a picture. The 15mm feed pipe and 22mm vent pipe from F&E cistern can be seen side by side between heating controls and Radiators wireless thermostat receiver shown on top right corner of the picture. I was thinking to run it only for a short period, maybe just hot water to the cylinder...
 
jorgemandrade said:
I have attached a picture. The 15mm feed pipe and 22mm vent pipe from F&E cistern can be seen side by side between heating controls and Radiators wireless thermostat receiver shown on top right corner of the picture. I was thinking to run it only for a short period, maybe just hot water to the cylinder...
Click to expand...
 

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DP said:
View attachment 335115

Look at this diagram, Are you sure the tee is out of sight?
Click to expand...
Yes the tee is out of reach. I have attached a picture of what I believe my system is which now makes me think. If that is correct, the only way to drain the Expansion tank is through the boiler because the pump is not running and the motorised valve is shut as I switched off the heating controls. Will the water just drain through the boiler if I have a drain hose connected to a radiator downstairs?
 

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jorgemandrade said:
Yes the tee is out of reach. I have attached a picture of what I believe my system is which now makes me think. If that is correct, the only way to drain the Expansion tank is through the boiler because the pump is not running and the motorised valve is shut as I switched off the heating controls. Will the water just drain through the boiler if I have a drain hose connected to a radiator downstairs?
Click to expand...
The area in question is the tee left of pump.

Regardless of tee being out of reach, the blockage most likely is there. Slow fall and rise of system water during heating cycles, along with originated water in the header tank, leads to buildup of sediment in that tee. Heating of water in the cylinder is effected as is draining down the system. At present, if the blockage is extreme, the expansion into the header will be from the vent pipe, leading to accelerated corrosion

Since system water has to pass through that tee, header will not drain no matter where you try to drain the system from. You could bail the water out of the cistern but that defeats the issue

Are you able to run heating without hot water zone switching on too?

Plenty written on the problem you are having as this is a common issue in combi boilers too which are sealed systems.
 
If the cold feed is teed into the vent then its a combined vent & cold feed system, but as stated, regardless, it will have to be cut out except there is a shut isol valve somewhere in the cold feed.
 
DP said:
The area in question is the tee left of pump.

Regardless of tee being out of reach, the blockage most likely is there. Slow fall and rise of system water during heating cycles, along with originated water in the header tank, leads to buildup of sediment in that tee. Heating of water in the cylinder is effected as is draining down the system. At present, if the blockage is extreme, the expansion into the header will be from the vent pipe, leading to accelerated corrosion

Since system water has to pass through that tee, header will not drain no matter where you try to drain the system from. You could bail the water out of the cistern but that defeats the issue

Are you able to run heating without hot water zone switching on too?

Plenty written on the problem you are having as this is a common issue in combi boilers too which are sealed systems.
Click to expand...
Yes I can run heating without hot water if need to but I'm concerned it might damage the pump as the system is pretty much drained. Could I refill the system using the vent pipe?
 
jorgemandrade said:
Yes I can run heating without hot water if need to but I'm concerned it might damage the pump as the system is pretty much drained. Could I refill the system using the vent pipe?
Click to expand...
Probably your only option to try if you can't sort the root cause and need to get things operational quickly whilst you work out what to do next.
 
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