Attic Central Heating Expansion Tank Overflowing

[JamesL85]

Hi,

I have a flat with a heating system approx 30 years old. I have a boiler in kitchen, hot water cylinder in airing cupboard and two tanks in my loft (a big cold water tank and a smaller central heating expansion tank).

In the last few weeks, the overflow from my central heating expansion tank began to steadily drip.

I called a plumber out, who suspected a faulty float valve in the CH exansion tank so they replaced it and set the valve to it would not rise too high.

A few days latter the drip returned. Taking a peak at the tank, it had filled back up to a level just above the lowest point of the overflow pipe, hence the drip.

If the central heating system is turned on, there can be a sudden stream of water shot out of the overflow pipe, before it eventually calms down and the dripping stops completely. Once the heating has been off a few hours, it starts to drip again.

Any ideas what could be wrong, and what I could do next?

Many thanks,

James

 

[doitmyself]

The coil in the HW cylinder has probably sprung a leak. The pressure from the cold water tank is then enough to send water through the leak into the coil, causing the water level in the expansion tank to rise.

Looks like it's new cylinder time.

 

[Reg Man]

Probably a pin holed coil in the hot water vessel. Is the small cistern lower than the big cistern? Is the water in the small cistern hot?

 

[JamesL85]

Thanks for your reply.

So in a fully working system, the coil has hot water circulating through it, and the rest of the cylinder has cold water in it that gets heated up? Then once a crack/leak appears in the coil, the cold water outside the coil then leaks through, which gets fed back up into the expansion tank?

Is there any simple way I can confirm a leaking coil before replacing the cylinder. I'm guessing it's a fairly expensive job?

Many thanks.

 

[JamesL85]

Probably a pin holed coil in the hot water vessel. Is the small cistern lower than the big cistern? Is the water in the small cistern hot?

The two tanks sit on an even platform. As the cold water tank is bigger, the water level of that tank is higher than the expansion tank. The water is normally cold when I check it, but that's often when the heating system has been off a while.

 

[glenno1]

Is hot water from your tap clear

 

[Reg Man]

Sounds like the coil then. The domestic storage cistern water level is therefore higher than that of the F&E cistern, so water will be forced through the holed coil and overflow the F&E. Remedy will be to replace the hot water storage vessel if this is the case.

 

[JamesL85]

Is hot water from your tap clear

Yes, it is.

 

[JamesL85]

How much would I expect to pay to get the cylinder replaced?

 

[doitmyself]

How much would I expect to pay to get the cylinder replaced?

Last year I paid £360+VAT to have a 36" x 18" replaced.

 

[Best]

If you tied the ballvalve up on the expansion tank & drained the water out of it & then watch if water fills up from the feed pipe in bottom of exp tank.

 

[stevetheplumber]

drain the cylinder run system see what happens if the small tank still fills its not the coil causing it, pin holed coils in my experience are quite rare it might be different in soft water areas

 

[tamz]

If it only happens when the heating is on it is a system problem.
Watch what happens at the tank when the heating is switched on.
It could be a circulaion problem forcing the level to rise or have you recently had the pump replaced?

 

[glenno1]

Is it definately a new ball valve and float that has been fitted(my suspicious side showing)

 

[Rob1811]

Have you tried geting someone to switch the heating on while you wait in the loft, to see what happens. Is it pumping over thro the vent pipe? Pos blocked cold feed?

 

[JamesL85]

Is it definately a new ball valve and float that has been fitted(my suspicious side showing)

Yes it was. The new ball valve was fitted in a low position, so it's now clear to see that although the the ball valve stops the water level filling up, it is filling up from one of the other inlets into the tank,

 

[JamesL85]

Sounds a good idea - it would at least prove the water is coming in through the pipe that comes up from the cylinder.

Problem is getting quotes of £600 to replace the cylinder...

 

[jam1979]

im with tamz could be pumping over worth a check

 

[Frog67]

Does your heating system have an anti corrosion inhibitor added to it? A build up of sludge in the system will cause the expansion tank to overflow as water will always take the path of lest resistance. Tell tale signs are dirty water and black deposits in expansion tank, dark brown or black water from radiator when bleeding, cold spots on radiators or frequent venting of certain rads. Hope this helps

 

[Rickster123]

Interesting first post frog. Welcome to the forum!

 

[stevetheplumber]

turn of the cold feed to the cylinder open hot taps try for 24 hours if that stops it the coils split

 

[Rickster123]

It's a 3 year old thread!

 

[tamz]

Probably ripped out and a combi stuck in under some eco scheme so there is a good chance that will be on its last legs too

 

[Unregistered]

Hi - thanks for the replies even a few years on!

I guess I can share the "this is how it ended story".

So basically the coil in the immersion cylinder had a hole in. The pressure difference between outside and inside the coil caused the overflow in the central heating overflow tank in the loft. Managed to get a good price on a new cylinder and fitting from a local plumber. Once that was done the problem was solved!

The next major DIY drama was fence-gate later that year, when all my fencing blew down in the October 2013 storm, but that's another story for another forum!

Thanks for all the advice on this thread!

 

[Reg Man]

Glad we were of some help to you.

 

[Frog67]

Isolate the large tank from the mains and drain it by running hot and cold taps in the bath. Run boiler if little tank stops overflowing then suspect split coil. If it continues overflowing then suspect fault in heating circuit. Bleed a radiator and if the water is brown/black then you probably have a corroded system causing restricted flow around the system and making the water travel up the coldfeed and possibly vent pipe.

 

[PlumbBobBob]

Isolate the large tank from the mains and drain it by running hot and cold taps in the bath. Run boiler if little tank stops overflowing then suspect split coil. If it continues overflowing then suspect fault in heating circuit. Bleed a radiator and if the water is brown/black then you probably have a corroded system causing restricted flow around the system and making the water travel up the coldfeed and possibly vent pipe.

Frog67 read post 24 above

 

[Frog67]

Doh! cheers steveb and thanks for the welcome APPlumbing