My central heating cold feed tank overflows continually; not ball valve; rad nearest pump always needing bleeding; lots of air in the system; when pump on it often streams out; set volume in cold feed to low, cleaned system out with Sentenal but still streams out; This all happened after heating was switched off last summer, emptied system, removed rad to decorate; then re-filled. Any thoughts?
C/H overflow continually
- Thread starter brianJ
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If cold water cistern in loft is above your heating header tank, the coil in your HW cylinder is leaking between the two systems. New cylinder required.
Prove it by stopping supply to heating tank (tie ball up if no stop cock)
Prove it by stopping supply to heating tank (tie ball up if no stop cock)
Given that it worked until you drained and refilled, let's start by assuming that nothing got broken in this short time. Your system is clearly full of air which expands every time you heat it up. It expands a lot, far more than that expansion tank was designed to cope with hence the overflow.
When everything cools down again it contracts. If you aren't watching at this point you won't see the ball valve open to replace the missing water. ChrisR's test is a good one though I would add one thing. Heat it up and let it cool but DON'T reheat until you've checked your tank level. Odds on you're going to find it empty.
If all this proves to be the case, you just need to get all the air out. Did you remember to bleed the cylinder heating coil? My trick for bleeding is to turn the boiler down to pilot only and pump cold water round the system. You might have to bleed and rebleed a few times before you get it all out. You can also expect to bleed for some time afterwards as the dissolved air comes out of that new water.
When everything cools down again it contracts. If you aren't watching at this point you won't see the ball valve open to replace the missing water. ChrisR's test is a good one though I would add one thing. Heat it up and let it cool but DON'T reheat until you've checked your tank level. Odds on you're going to find it empty.
If all this proves to be the case, you just need to get all the air out. Did you remember to bleed the cylinder heating coil? My trick for bleeding is to turn the boiler down to pilot only and pump cold water round the system. You might have to bleed and rebleed a few times before you get it all out. You can also expect to bleed for some time afterwards as the dissolved air comes out of that new water.
I've not see that volume of air be stuck for any time. It would get stuck in the rads then not really heat up.
Brian when you say Overflow, you do mean like out of the house, yes?! Not just the vent pipe which is over thetank, dribbling back into the tank.
Brian when you say Overflow, you do mean like out of the house, yes?! Not just the vent pipe which is over thetank, dribbling back into the tank.
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When the C/H ot H/W is on, the water appears to come from the cold feed at the bottom of the tank (feeding the system) and not the vent pipe or the ball valve. It is like it is rising up from the system. At the moment, the C/H and H/W is on and the overflow pipe outside the house is continually dripping. I hear the boiler stat kick in and boiler fire up and a little while later the water is streaming outside my house. When the heating is switched off it drips very slowly and sometimes stops completely (I'll double check this last point). Will try tests suggested and put an update soon. Thanks for your help.
Test 1 - Turned off C/H and H/W at boiler. Outside overflow slowed to a drip. Water level in C/H header tank did not recede. Water continued to drip slowly.
Test 2 - Tied up the ball valve in the H/W & shower header tank. Turned the H/W taps on to drain the water level to below the C/H header tank. Outside overflow from C/H header tank stopped. lowered the water level in the C/H header tank to a few inches above the bottom cold feed to C/H system and turned only the C/H on the boiler (H/W switched off still). Water level did not rise much. Just a little expansion. Released the ball cock in th H/W header tank and let it fill back up. Turned on both C/H and H/W. Since Thursday afternoon right through until 10:00 Friday, the C/H has been on, then off through the night, then back on this morning and the level of water in the C/H header has not risen. It's not dripping on the overflow and now completely confused. The overflow would usually be dripping within 1/2 day of empting the C/H header tank. Will leave the C/H & H/W off now until Sat PM then check level again when switched back on.
Test 2 - Tied up the ball valve in the H/W & shower header tank. Turned the H/W taps on to drain the water level to below the C/H header tank. Outside overflow from C/H header tank stopped. lowered the water level in the C/H header tank to a few inches above the bottom cold feed to C/H system and turned only the C/H on the boiler (H/W switched off still). Water level did not rise much. Just a little expansion. Released the ball cock in th H/W header tank and let it fill back up. Turned on both C/H and H/W. Since Thursday afternoon right through until 10:00 Friday, the C/H has been on, then off through the night, then back on this morning and the level of water in the C/H header has not risen. It's not dripping on the overflow and now completely confused. The overflow would usually be dripping within 1/2 day of empting the C/H header tank. Will leave the C/H & H/W off now until Sat PM then check level again when switched back on.
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Hmm guess what! i have same problem with F&E tank dripping.
Baxi burmuda 401 boiler, indirect system.
Ball cock replaced in F&E tank, still drips.
Afte bailing out F&E tank it takes a couple of hours to refill to a dripping overflow
I have had a container suspended over the vent pipe that comes from the boiler and hangs over the F&E tank, that stays empty but the level in the tank still rises.
Thought it might be due to expansion so swithched off C/H and H/W shut of cold water supply to house and allowed system to cool down..
Still dripping! so i guess (but not too sure) that it is most likely a leaking coil in hot watewr tank??
Or could it be the heat exchanger in the boiler...
as a replcement H/W tank is going to be around £350 replaced, i would like to be a bit more certain.
Any ideas???
Thanks
Baxi burmuda 401 boiler, indirect system.
Ball cock replaced in F&E tank, still drips.
Afte bailing out F&E tank it takes a couple of hours to refill to a dripping overflow
I have had a container suspended over the vent pipe that comes from the boiler and hangs over the F&E tank, that stays empty but the level in the tank still rises.
Thought it might be due to expansion so swithched off C/H and H/W shut of cold water supply to house and allowed system to cool down..
Still dripping! so i guess (but not too sure) that it is most likely a leaking coil in hot watewr tank??
Or could it be the heat exchanger in the boiler...
as a replcement H/W tank is going to be around £350 replaced, i would like to be a bit more certain.
Any ideas???
Thanks
cylinder is shot 
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Thanks kevplumb for your rapid reponce!!!!
I am certainly inclined to agree wth you!
do you know of anything else i could try before i part with £350??
The reason i seem uncertain here is becouse i have had a plumber round (not a central heating engineer!) who is quite prepared to change the tank for me but he seems reluctant to say that it is definatley the problem (fair enough) and suggests i have the boiler serviced first.
I dont realy want to end up paying for both jobs if one will do..
I am certainly inclined to agree wth you!
do you know of anything else i could try before i part with £350??
The reason i seem uncertain here is becouse i have had a plumber round (not a central heating engineer!) who is quite prepared to change the tank for me but he seems reluctant to say that it is definatley the problem (fair enough) and suggests i have the boiler serviced first.
I dont realy want to end up paying for both jobs if one will do..
servicing the boiler wont stop an overflow
if you want to be sure empty the f&e tank isolate the water supply to it
if it then fills where else is it coming from
part with big wad of cash and
if you want to be sure empty the f&e tank isolate the water supply to it
if it then fills where else is it coming from
part with big wad of cash and
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Thans again kevplumb for you rapid reply and advice..
I actually did what you sugested this morning..
Swithed off C/H and H/W.. turned off stop tap. (F&E level below overflow) and after an hour or so, Drip drip drip again
So thanks for comfirming my suspisions.. i guess its get the money out time!!
I actually did what you sugested this morning..
Swithed off C/H and H/W.. turned off stop tap. (F&E level below overflow) and after an hour or so, Drip drip drip again
So thanks for comfirming my suspisions.. i guess its get the money out time!!
If it's a leaky heating coil in the tank - and this now looks very likely - then it must be a small leak. That could explain why it appeared only after you drained the heating system. (A coil full of air tries to float to the top and that puts a strain on any pre-existing weak spot.)
With such a small leak it could come and go possibly depending on water temperature. You've shut off the F/E tank supply so it's not coming in there. You've observed it filling up and overflowing with no heat input anywhere (including immersion heaters???) so it's not expansion. There is no other point at which water can enter your heating system (only you can confirm that). Conclusion; your heating coil leaks.
Here's the definitive test if you can do it. Lower the water level in your storage tank until it's BELOW the F/E tank. Drain it right down to hot tap level if you like. Does the water in your F/E tank go DOWN? QED.
With such a small leak it could come and go possibly depending on water temperature. You've shut off the F/E tank supply so it's not coming in there. You've observed it filling up and overflowing with no heat input anywhere (including immersion heaters???) so it's not expansion. There is no other point at which water can enter your heating system (only you can confirm that). Conclusion; your heating coil leaks.
Here's the definitive test if you can do it. Lower the water level in your storage tank until it's BELOW the F/E tank. Drain it right down to hot tap level if you like. Does the water in your F/E tank go DOWN? QED.
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