Overflow from Feed and Expansion Tank

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I seem to have a problem, or combination of problems, with my central heating / hot water system. It is a fairly conventional pumped system, oil-fired boiler, pump, two 2-way valves, HW cylinder, radiators, F&E tank in loft (base same level as cold water tank, so F&E water level well below cold water tank level). Usually it works OK (rads and hot water).

For some time (months) the feed and expansion tank overflow has sometimes been dripping outside, and looking at the tank months ago, I saw that the expansion vent (inverted J) pipe was dribbling hot water, and the tank was full to the overflow level. I tried changing the pump speed, and that seemed to help a bit, but not cure it, but as the problem was intermittent, I couldn't be sure if it made much difference.

I have moved some radiators around over the last few months, but the problem occurred before and after, so I don't think it's relevant.

Last weekend I decided a bit more investigation was required, and replaced the F&E ball-valve, replaced the float (it had water splashing about inside), drained the system a bit, and adjusted the arm so that the tank (with the system cold) was perhaps less than a quarter full. My theory was that the water in the expansion vent pipe would be hotter (less dense) than in the feed pipe, and I needed a greater difference between the top of the vent pipe and the water level in the tank. I also bled the rads.

In the spirit of unjustified over-confidence and with the level steady in the F&E tank, I was pleased with myself.

Now the problem (or problems) seem to be worse than ever, and I could hear it dripping at midnight last night, and looking at the ceiling below the tank, I could see an ominous wet patch, right over "she who must be obeyed"'s clothes cupboard. Into the loft, where I found that I must have disturbed the overflow pipe, and it was no longer fully connected to the tank, and the tank had filled up again. I closed off the isolation valve for the ball-valve, switched the CH controller off, and drained the system, ideal pastimes for that time of night!

At the moment, I've closed off the drain valve, but kept the ball-valve off, and I'm waiting to see if the system fills up slowly, suggesting a leak in the coil in the HW cylinder.

I have checked other similar posts, and a frequent suggestion is the wrong arrangement of feed/vent/pump. I have got (as far as I can tell, as I didn't install it):

22mm from boiler to T piece
T piece has 22mm to vent over F&E tank and about 150mm of 22 mm to another T piece
This second T piece has 15mm to the feed in the F&E tank and 22mm to the pump
The pump goes to another T piece, then to the two 2-way valves

Another suggestion is wrong direction pump - mine has an arrow pointing from the boiler supply (via the T pieces) to the 2-way valves.

Another suggestion is blockage in the feed pipe. When I drain the system, the tank level drops quite quickly, so it's not blocked in one direction, but not sure about the other direction.

Another suggestion is the boiler is boiling, or at least too hot. When I refill the system, I'll try a lower setting.

I'll also flush the system.

Does anyone have a theory about how these all may be linked, or have I had several problems at once, and what should I try next?

Perhaps I should just do a loft conversion, as I'm spending so much time up there!

Thanks in advance for any assistance.
 
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Sounds very much like the coil has failed inside the hot water cylinder. If you turn off the mains water supply to the feed tank and the water level still rises that is the answer.
 
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Sounds like you have a cross vented "h" system & the cross piece is blocking up so the pump is pulling water out of f & e tank hence pumping over. Best bet is to drain system remove "h" arrangement fit an air seperator then powerflush system
 
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weareleeds said:
Sounds like you have a cross vented "h" system & the cross piece is blocking up so the pump is pulling water out of f & e tank hence pumping over.
I am showing my ignorance of course, but can you explain what this means in slightly more layman's terms. The "H" that I have in the airing cupboard is:

bottom left 22mm from boiler
top left 22mm to vent over F&E tank
horizontal part of H is ~150mm long
top right is 15mm feed from F&E tank
bottom right is 22mm to pump

Are you saying a blockage in the 150mm horizontal section? Any unblocking tips, e.g. turn the pump on and off repeatedly, or swap the pump round temporarily to reverse the flow, or drain it all and unsolder?

In the meantime, I'll wait to see if the level goes up with the F&E ball valve isolated...which would mean the coil? Or more than one problem? :confused:
 
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If you have a small magnet handy try touching it to the pipework around the H arrangement. If the magnet sticks to the pipe that is a sure sign of blockage or heavy deposition of iron oxide inside.

Regarding the possible failed coil in the HW cylinder check to see if the ballvalve serving the main CW tank dribbles even after a long period of no water being used. If so and the level rises in the F&E tank the coil is shot and a new cylinder is required.
 
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No indication of blockage with the magnet trick, but I guess there could be non-ferrous blockage.

Cold water tank ball-valve does drip slowly but steadily, perhaps one drip every few seconds, and doesn't overflow, but then perhaps a big tank always get some water taken from it often enough that it wouldn't overflow with a slow drip rate from a leaking ball-valve. I've tried pushing the arm down so the tank tops up a bit, and then it doesn't seem to drip, so I don't think the drip is a leaking ball-valve, suggesting it is topping up as a result of a coil leak.

I can't detect any rise in F&E level yet, maybe ~10mm, but then I haven't switched the system on, so it's probably got various air pockets in it until it gets pumping, so perhaps the level hasn't settled yet. I have bled the radiators. My thought is that if I switch the system on, the level will rise because of expansion, and then I won't be able to tell if it's rising because of a coil leak, so I don't want to switch on yet. Is there any merit in switching the system on but the boiler off, so that the pump will get the air moving and I can bleed it out, then have a steady system to monitor for any rise?

So a failed coil seems the most likely, but as it is the most expensive and time-consuming and disruptive, I don't want to jump to that conclusion.
 
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You will know if it is a coil leak because it will rise up the cold feed pipe to your small f/e tank and you won't see it filling until it comes out the overflow.
This will sometimes only happen when the boiler is running and the coil expands thus opening the split. ;)
 
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bobthebender said:
This will sometimes only happen when the boiler is running ... ;)
I'll switch it on then, and discover the joys of running the central heating on one of the hottest days of the year!!
 
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RickRandom said:
bottom left 22mm from boiler
top left 22mm to vent over F&E tank
horizontal part of H is ~150mm long
top right is 15mm feed from F&E tank
bottom right is 22mm to pump

Doesn't sound that anything is piped wrong here, but I would fit a Mysom aerjec instead of the 'H' arrangement as previously suggested. I've known these to cure 'your problem' even though the existing pipe work looks ok.
 
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wilhelm

maybe it is boiler stat. and youve got a thermal reset hi limit stat, so you would not really be aware, apart from maybe light on boiler that it has gone to limit.

boiler is?????????
 
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wilhelm said:
maybe it is boiler stat.
Thanks for the suggestion. Boiler was serviced a month or so ago. Looking at the report, nothing on thermostat performance, (all about oil burner) but the boiler over-temp light isn't on, and I just nudged the stat control on the boiler up a tad, and the boiler fired up, so my thoughts are it's probably OK. (Unless my evaluation method is rubbish?)

Still waiting for the F&E tank level to change to prove the leaking coil theory....it's probably a case of "a watched kettle won't boil". I expect I can guarantee a catastrophic failure if I go away for a couple of days.

At the moment F&E level is steady, perhaps up 20-25mm since I switched the boiler on, and there are occasional bubbles from the feed, so the "H" configuration is allowing air out to some extent. There is nothing coming out of the vent.

Also when I switched the boiler on, the 150mm long horizontal part of the H got warm at about the same time as the pipe from the boiler and the pipe to the pump, which would suggest it isn't blocked. (The feed and expansion upper parts of the H didn't get warm as quickly, although they are hot now.) The water in the F&E tank is cold.

But I'm certain of nothing at the moment.
 
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wilhelm

what im saying is, the light will be on when its tripped, but if its thermal reset, once boiler cooled, it will rest automaticaslly and put off light.

like i might put your lights out for not telling what fkn boiler it is. ;) it matter not.

if its a boulter.then very common, i carry them in me trouser pocket. :LOL:
 
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Boiler is Trianco TRO 12/14 Mk3.

Sorry, I should have said, and I shouldn't have edited the earlier post. :oops:
 
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wilhelm said:
boiler is?????????
Doh! Now I understand. I thought you meant "boiler is knackered/kaput" and the ????? were just a replacement for an expletive, not "boiler is what make?".
 
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wilhelm

not changed any of those, except early editions.

i would be tempted to turn stat to much lower position, and see what happens.
 

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