CH f&e tank overflowing

[dom_trig]

Hi,

Complete newbie but want to gain an understanding of what the problem might be before getting the pros in.

Background:

Solid fuel (anthracite) boiler for central heating (pumped) and gravity fed dhw, open vented, indirect cylinder. Recently noticed water coming out of downspout at front of house. Further investigation revealed that the overflow pipes from the f&e tank and cold water storage tank led into gutter and hence through downspout. Both tanks were overflowing. Removed excess water from both (water was cold). Cold water storage tank has had no further problems. However f&e tank keeps refilling with cold water. After monitoring for a few nights, it appears that the cold water is coming from the feed (ball valve okay, no water from coming from vent, no steam etc.). I have tried turning down the pump but this has had no effect. This system has been working fault free for three years. The only change/work is that we had a radiator temporarily removed and has since been replaced and had the boiler serviced. However I cannot see how this would cause the overflow. Looking around on the forums it appears that this may be a pinhole in the coil in the hw cylinder. However there is no discolouration/nasty stuff in the hotwater. I want to exhaust all other possibilites before replacing the cylinder.

As we have solid fuel boiler, temperature control on the water is minimal, could it be that the boiler is overheating the water causing excessive expansion?

Any ideas or further things to investigate would be appreciated. if all else fails then I think will have to fork out for new cylinder.

Many thanks in advance

Dom

 

[easyt]

You say ball valve OK.
Do a simple test. Hang a plastic bottle (top cut off) under expansion pipe. Leave for a day and check what has come out. If it is overflowing when hot water/heating off then it must be valve of course. Has there been any works by water authority in the area. I know that my water pressure increased after recent works.

 

[dom_trig]

Hi Easyt,

Definately not the expansion pipe, I took the water out of the f&e tank and monitored over the period of a couple of hours, no water coming from there. No works in the area that I know of.

Any more ideas??

 

[easyt]

If it is just the F & E tank I would suspect the valve.

There are only four ways water can get into the F&E tank that I can think of.

1. Through the hot water expansion pipe. You say not.

2. Through a leaking inlet valve on the ball valve (or due to a punctured float making the float less bouyant so that the water fills to a greater height).

3. a leak in the heating coil in the hot water cylinder allowing tank fed mains and the sealed heating circuit water to mix. When the heating is on and pump running it could push water out of the heating system and into the cold water tank. I suppose heating pump is off the opposite could happen if your water surface level is higher in the cold water storage tank than in the F & E tank.

A leak in the roof and no cover on F&E tank

I am not a plumber or heating engineer but can think of no other alternatives. Hope it's your valve but you did say it had happened to both tanks.

As I said before you could have had a temporary increase in water pressure causing both ballcocks to leak and the one to the F&E tank might have got some muck under the seal. But you say it is not leaking.

Take some water a bit at a time out of your F&E tank until the inlet valve just starts to drip. Watch and make sure it reseals - mark or measure the water level. Make sure your heating is off - no pump- and see if the level goes up.

I can think of another highly unlikely possibility.

 

[darrenangel]

the f&e tank is used for expansion within the central heating circuit and so the level with rise and fall as the circuit is in use.This expansion is allowed via the feed pipe but if the ball valve is set to high to begin with, it will overflow as the water heats up.

 

[easyt]

True Darren but why it should be overflowing now if not before? I suppose his best bet with that is to adjust the float to a lower level and monitor

 

[dom_trig]

I've inspected the ball cock again, there is a very slight drip, but not at the rate that could fill the f&e tank as quickly as it has been doing.

I will try bending the arm on the ball valve and set the water level lower and see if this works. As the boiler is solid fuel, there is always an element of heat in the system.

Is there any fool proof way of ascertaining if the coil in the cylinder has a leak? One would assume the that the mucky water from the ch circuit would be discolouring/affecting the dhw. Is this logic correct?

 

[easyt]

I doubt it is the coil. If there is a slight drip at the ballcock that could be enough to let the tank fill just too high. If it were the coil I aam sure you would notice some discolouration.

 

[easyt]

Expansion is not normally great but I suppose if you had air in some radiators then as air expands much more than water this could cause a greater rise in F&E