Water overflow pipe running

[JeffT]

Hi I'm pretty sure I know what the problem is but just wonder if somebody could advise. The central heating system is 25+ years old with pumps, valves etc being replaced at intervals. The system has a boiler with indirect hot water & pumped CH with a header tank in the loft. I have a water softener which has been in for 20+ years

The symptoms are as follows:-

1) The cold water tank overflows even though the ball valve is working properly.

2) The CH header tank seems to often have a drip fill from the ball valve.

3) After 3 weeks holiday with no domestic water use the domestic hot water & cold water was brown. (the boiler went out but I think that is a different problem as its stayed alight for the past 3 weeks)

4) When the heating / hot water is turned off (pump off) the water stops flowing from the overflow.

Without item 4) I'd say that there is a pinhole in the HW heating coil. With item 4) I wonder if a pinhole could only be operating when the pump is running, with no back flow which would fill the CH header tank when the system is off? How likely is that?

Could the brown colour be from the CH water contaminating the domestic or would it be some bug growth

Hope somebody can help

Jeff

 

[easyflow]

sounds like coil in cylinder is split/holed and mixing with domestic supply.
New cylinder

 

[JeffT]

Yes thats what I think.

But why doesn't it fill the CH header tank when the boiler / pump etc is off. The water level in the Domestic Cold storage is higher than the CH header tank, simply because the bottom of each is at the same level, but the CH header tank is smaller. I'd have thought that the water levels would try and equalise. Its as though there's a non return valve in the leak?

J

 

[Nige F]

Hi I'm pretty sure I know what the problem is but just wonder if somebody could advise. The central heating system is 25+ years old with pumps, valves etc being replaced at intervals. The system has a boiler with indirect hot water & pumped CH with a header tank in the loft. I have a water softener which has been in for 20+ years

The symptoms are as follows:-

1) The cold water tank overflows even though the ball valve is working properly.

2) The CH header tank seems to often have a drip fill from the ball valve.

Could the brown colour be from the CH water contaminating the domestic or would it be some bug growth


Jeff

1 ) fit a new ballvalve 2 ) Fit a new ballvalve

 

[Nige F]

because the bottom of each is at the same level, but the CH header tank is smaller.
J

It won`t flow uphill the brown could be coming out of the mains water supply pipe

 

[JeffT]

Thanks Easyflow & Nige F.

I have changed the ballvalves and these are not leaking. I think the drip in the CH header tank is because the water is being lost into the Hot water cylinder through the leak and then leaving through the cold water tank overflow as this is where the hot water expands into. I think the flowrates out of the overflow & into the header tank differ because the Hot water is being heated therefore expanding.

I suppose the brown staining of the water could have come from the mains but the mains water is clear. It isn't noticeable in normal use in the stored water just after its been standing for a few weeks. Whilst, if the slow leak is occurring, this would be putting mains water in the heating system which migrates into the hot water tank then the cold water storage tank and finally out of the overflow, if the mains isn't brown then it still wouldn't be brown. I have a theory that if the water is softened then it could still be dissolving original scale which could be brown, I'm not sure if there would be much limescale after 20+ years of softened water. I think the brown is more likely coming from the CH system and is probably rust as my inhibitor will have long gone if there's a leak.

I still don't know why I don't get a back flow into the CH header tank when everything is static. I can only think there is still some scale in the tank which is covering the leak. This is pushed open by the pump pressure but closed by the differential head between the two tanks in the loft when nothing is working. I'm not sure how likely this is but I guess it doesn't really matter. A leak is a leak and needs repairing.

I'll probably wait a few weeks & hopefully the weather will be warmer then replace the cylinder.

Thanks for all your help

Jeff

 

[Nige F]

The vent pipes could be over the wrong tanks in the roof trace then back to the c/heating and the hot cylinder

 

[JeffT]

Hi Nige F

No the vents are OK I put the plastic tanks in years ago so know exactly whats connected to what, & nothing has ever come out of the vents either. The only explanation I can think of is a leaky coil in the HW cylinder.

At this very moment the CH header tank has one drip every 3 secs from the fill valve & the CW storage tank is at the normal level. The hot water heating valve is off so probably the main pump flow is through the heating circuit. The drip is probably what is leaking into the hot water cylinder backflowing from the return pipe.

I think its a very small leak though exacerbated when the water is pumped through the coil.

I'll change the cylinder & hope it stops. I really can't think of anything else it can be as its the only place domestic stored water & CH water come into close proximity. If it was worse I could probably be more sure, but I don't really want it to be worse.

Thanks for the thoughts. If you do think of anything else which may mean its something else I'd be happy to hear. I don't relish the thought of changing the cylinder but I'm sure it'll go OK.

Jeff

 

[Nige F]

I`d hate to have to replace a cylinder - unless it`s old/unlagged /grade3 with a crappo heat ex. coil I would isolate the heating from it and rig up a water pressure test on the coil from the mains water , some plastic pipe and a pressure gauge - filled up - isolated and watch the gauge In the Summer if we get any

 

[JeffT]

Nige F

Yes I know. The cylinder is foam insulated not sure of the grade etc but its lasted 26 years with me living here. Probably installed by the last occupant. Problem with doing any testing is that the connecting valves have frozen so I have to drain the whole system down to disconnect anything. I've tried WD40, heat, spanner & screwdriver at the same time but I guess they're like me old & stiff.

Similar with the boiler an old Thorn Apollo. Having a few issues with that at the moment as well, but I think its the pump over run stat wired the wrong way round. I wish they wouldn't change the terminal locations, replacing things are easy but generic parts don't sometimes have the same layout. Just about to look at the wiring diagram to see if I can sus out which of terminals 2 or 3 should be connected when cold to terminal 1.

At least I have the time, retired at christmas, but I did really want to do other things

Thanks for the advise

Jeff