Feed And Expansion Tank Loosing Water?

[Thedud2010]

Hi all,

Not a whizz with central heating as I am an IT network administrator by day so in need of a bit of help.

My ch system is an open vented system with indirect hw cylinder.

In may this year we had a rad leak in the bedroom and replaced by british gas.

Came back of holiday to a cold england a couple of weeks ago and the mrs switched on the heating on. Heard some noises in the pipes so decided to switch it off and have a look in the loft.

The feed and expansion tank was empty or below the level of the fill pipe thus was drawing air into the system it seems as though the cold feed tap was turned off so I turned this back on and filled up the tank and once full switched on the system to draw the water in.

After an hour or so checked all the rads all hot so all ok. I checked the tank and it was full still and the heating has been fine. I decided to switch off the cold feed so I could see if more water was being drawn into the system to replace any air.

After a week I checked the tank and the water level had dropped in the F&E tank by 2 inch's. So I turned the cold feed on again and let the tank fill again and cycling the heating again for a few hours.

Once again I have turned off the cold feed so I could visually see if more water was being drawn in. I have now monitored it for 2 weeks and every night it is dropping about an inch. What I cannot understand is where the water is going as all the radiators are hot there cannot have been that much air in the system could there?.

We have looked everywhere and cannot see any leaks in the house. I did think could it be possible that the hw cylinder heat exchanger could have fractured inside and it is going that way, however I have checked the vent pipe from the hot water cylinder which leads back into the cold feed tank (big tank) and could not see any water going over.

Any ideas?

I have british gas homecare cover but dont want the agro of calling them in taking time off work & look like a wally in the process as I dont what the problem is

Thanks

Lee

 

[seco services]

I have checked the vent pipe from the hot water cylinder which leads back into the cold feed tank (big tank) and could not see any water going over.

if it was passing to the dhw it wouldn't come out the vent pipe anyway it
would come out the cold feed to the cylinder (pipe in bottom of cws)
and that would only happen if your f/e tank is higher than the cws tank.

what is the position of each of your tanks ?
is your cws water warm/hot at all ?

 

[wiss]

If your coil has gone in your cylinder the lower of the tanks will overflow, normally the f&e tank is lower so a cracked coil will result in the f&e tank to overflow, have you got any under floor pipework???

 

[seco services]

If your coil has gone in your cylinder the lower of the tanks will overflow

not if it's the cws and the f/e is only loosing an inch aday.
you use more than that aday from the cws.

 

[Thedud2010]

Hi,

Thanks for the replys, my tanks are in the loft both at the same level sitting ontop of a wooden support spanning two beams in the loft.

The water in the cws (big tank) is cold. Neither tank is overflowing.

The only part of the house which is has under floor pipe work is the upstairs as downstairs is a solid concrete base so the rads downstairs have pipes dropping down which are inside the wall so if they were leaking I am sure I would have seen something from them. There is no visible sign of leaks however I was thinking of taking up floorboards up at the weekend to check them in the bedrooms and bathroom.

Lee

 

[seco services]

Hi,

Thanks for the replys, my tanks are in the loft both at the same level sitting ontop of a wooden support spanning two beams in the loft.

so the f/e water level will be lower than the cws.

which are inside the wall so if they were leaking I am sure I would have seen something from them.

are they block or stud walls ?
and not always visable.
how long has this been going on do you think ?

 

[Thedud2010]

Your right, I believe the F&E level will be lower than the cws but probably not by much.

The walls are plasterboard dot and dabbed on breezeblock think they have used 10mm pipes to rads and put this inbetween the plasterboard and the breezeblock.

We have only just started to use the central heating again as when bg fixed the rad it was practically summer and the heating was not really used after. Over the summer the boiler has been heating hot water only so this is what lead me to think the hw cylinder has a problem as it has emptied the F&E tank over the summer the valve closing the heating circuit and just heating the hw cylinder.

It maybe more obvious now as I am keeping an eye on the levels and noticing what is going each day that and the mrs is putting on the heating before I get in from work (even though it is not cold yet!)

I think the spare bedroom is a little damp aswell tonight but we have had the washing out so maybe a coincidence.

Thanks

Lee

 

[wiss]

Has your f&e tank got a lid?? if youve left the cold main to the tank off you could be loosing a bit through evaporation, especially if theres a problem with pumping over the vent as the water will be hot.... just a thought,

 

[Thedud2010]

Yeah F&E tank has a lid & insulation padding around it all. It does pump over quite a bit and the water is quite hot steam when I open the lid to check it(if the heating or hot water is called).

 

[seco services]

It does pump over quite a bit and the water is quite hot steam when I open the lid to check it(if the heating or hot water is called).

now where getting some where if the f/e vent is pumping over thats useally a sign of a restriction or a blockage in the system ie sludge etc.
whats the condition of the water in the bottom of the f/e ?
what speeds the pump on ?

 

[Onetap]

After a week I checked the tank and the water level had dropped in the F&E tank by 2 inch's. So I turned the cold feed on again and let the tank fill again and cycling the heating again for a few hours.

Hang on; it is an expansion tank, so the water level is meant to rise when the system is hot and the level drops again when the system is cold.

When you have checked the level, has the system always been cold?

The water level should be 2 or 3" above the level of the cold feed outlet with the system cold. When hot, the water level should not come close to the overflow outlet connection. An F&E tank incorrectly set-up (as a storage cistern) will cause big corrosion problems.

You have corrosion problems (radiators are NOT consumables, they should NOT rust) so it looks like it may be a longstanding, unnoticeable leak.

If it is losing water, then it's probably a leak under the floor, into the CWS cistern, into the boiler combustion chamber, out of the boiler pressure relief valve (if there is one), etc.. You could get a leak into the CWS cistern (despite the F&E level being lower) if the pump is pressurizing the DHW cylinder coil; a slow leak wouldn't necessarily be noticeable since the water will be drawn off in normal usage.

PS I missed this bit;

"It does pump over quite a bit and the water is quite hot steam when I open the lid to check it(if the heating or hot water is called)."

Well it shouldn't, so get it sorted. It is causing the corrosion and probably accounts for the 'leak' by the evaporation. It will also cause condensation in your loft and make the timbers liable to woodworm infestation and rot.

 

[Thedud2010]

Many thanks for the replies,

I have tonight done a little test to see if the coil has indeed got a problem inside the cylinder. I ran all my hot taps for 20 minutes, while the system is cold and I switched off the power to the boiler to be sure, this was to draw water through the system and then I kept an eye on the f&e tanks level to see if it went down and it did by 1cm ish.

This problem has been ongoing for a couple of weeks now that I am aware of however may have been like this all summer since rad was replaced as ch was off. My guess is if I had a leak I would have seen it around the house at some point especially it is was upstairs as the amount of water that has dissappeard out of the F&E tank would have certainly made a mark somewhere.

As I have the BG cover I will call them in and tell them everything I have done up to this point and see what transpires.

Hang on; it is an expansion tank, so the water level is meant to rise when the system is hot and the level drops again when the system is cold.
When you have checked the level, has the system always been cold?

I have checked the level when system is hot and cold however the level never comes back up it is dropping and because I have switched off the cold feed to the F&E tank otherwise it would be topping it up continuously.

The water level should be 2 or 3" above the level of the cold feed outlet with the system cold. When hot, the water level should not come close to the overflow outlet connection. An F&E tank incorrectly set-up (as a storage cistern) will cause big corrosion problems.

By cold feed outlet I am guessing you mean the feed pipe to the CH system if this is the case then it is 3" above it and the water level has never come close to the overflow however when I returned on holiday the tank was completly empty below the level of the feed (only because the mains feed had been switched off) had this not been the case there is a good chance I would never have noticed the problem.

You have corrosion problems (radiators are NOT consumables, they should NOT rust) so it looks like it may be a longstanding, unnoticeable leak.

It may well be however it has never emptied the F&E tank before as it did while I was away never had trouble with it since we moved in 5 years ago.

If it is losing water, then it's probably a leak under the floor, into the CWS cistern, into the boiler combustion chamber, out of the boiler pressure relief valve (if there is one), etc.. You could get a leak into the CWS cistern (despite the F&E level being lower) if the pump is pressurizing the DHW cylinder coil; a slow leak wouldn't necessarily be noticeable since the water will be drawn off in normal usage.

My guess at the minute is as you said a small leak into the hwcylinder not noticeable as the draw during the average day is compensating so no overflow.

PS I missed this bit;

"It does pump over quite a bit and the water is quite hot steam when I open the lid to check it(if the heating or hot water is called)."

Well it shouldn't, so get it sorted. It is causing the corrosion and probably accounts for the 'leak' by the evaporation. It will also cause condensation in your loft and make the timbers liable to woodworm infestation and rot.

The lid is on tight it is not steaming up the loft but I agree there is a problem that needs recifying but we are thinking of moving dont really want to shell out for a new system/flush reconfiguration if I dont have too. [/quote]

 

[wiss]

If you h/w cylinder coil has gone then your f&e tank would overflow - not lose water,

you did say both tanks are on the same level base didnt you??? so the cws water level will be the higher.

I wouldnt think its the coil personally.

 

[foxhole]

When you turned on water [first post] did you bleed the rads? if not the system has lots of air in it and as it migrates out the level will fall in the feed tank.

 

[Thedud2010]

When you turned on water [first post] did you bleed the rads? if not the system has lots of air in it and as it migrates out the level will fall in the feed tank.

The rads all get hot at the top so I figured the rads are ok. Will go round and bleed them today and get back to you to make sure. Only problem I have is the previous owners painted all the rads with matt paint and its difficult to open them all.