Overflowing HOT water SUPPLY header tank.

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NOTE:- THIS IS NOT THE CENTRAL HEATING FEED/EXPANSION TANK.
Hi,
I have a gas gravity fed hot water and central heating system with a freestanding boiler in the garage. The system has an indirect hot water (HW) cylinder with a standard pumped central heating (CH) system. The
house (HW) circuit has its own dedicated 25 gallon hot water feed/expansion (Header) tank which is in the loft under which is located separate 4 gallon dedicated CH/Boiler feed/expansion (Header) tank, the HW header tank is approx 60 cm above the boiler header tank, both have their own separate mains water supply, feed and expansion pipe work. This system has been untouched and working perfectly for the last twenty or more years (With minor maintenance and normal servicing). Three weeks ago, I noticed that the HW header tank was overflowing, I replaced the ball cock washer but next morning it still overflowed. I replaced the ball cock completely but unfortunately, it still overflowed. I turned off the water supply to the ball cock, however next morning the tank was full and still overflowing. Since then I have carried out a series of tests to establish where the excess water is coming from.
1) Turned off the boiler (Via the central heating programmer, pilot light still running) - HW TANK STILL OVERFLOWING.
2) Turned off the boiler plus turned of the mains water supply - HW TANK STILL OVERFLOWING.
3) Turned off the boiler plus turned of the mains water supply plus hung a container under the HW (Cylinder) expansion pipe – HW (CYLINDER) EXPANSION PIPE CONTAINER DRY - HW TANK STILL OVERFLOWING.
It would seem that the only place that the water can be coming from is up the HW (Cylinder) gravity feed pipe?
Tonight I will repeat (3) above plus turn off the HW (Cylinder) feed pipe supply, this should result in no additional water entering the HW header tank.
All the while that this problem has existed the house CH (CH programmer) has been off. At all times the water level in the CH/Boiler feed/expansion tank has remained completely normal.
It should be noted that this system is a very basic with no diverter, 3-way, or zone valves in the system.
In addition, no immersion heater was switched on during any of these tests (I unplugged this at the start to be sure).
Question.
Should I confirm that the excess water is coming into the HW header tank via the HW (Cylinder) gravity feed pipe has anyone any idea what may be causing this problem?
Initially I thought that this may be due to a failed indirect coil in the cylinder. However I cannot see how this could be the case when the water is able to push uphill into the header tank, some six feet above it, particularly knowing that this happens when the boiler is COLD, with no pressure in the circuit caused by heating.
I am baffled; any suggestions would be greatly appreciated.
 
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It is not unknown for cold water to pass through a mixer tap or a shower valve body and back up the hot supply, especially if the cold feed is at mains pressure.

I have heard of a cold feed only washing machine wrongly connected to both hot and cold feeds via a 'Y' piece. That allowed mains pressure cold water back up the gravity hot feed.

If the central heating F&E tank is above the CWST, then a failed coil is a possibility. With the F&E tank is below the CWST, a failed coil would cause the heating F&E tank to overflow.
 
Firstly let me apologise for not including my name “Garry” in my request.

Thanks to both TicklyT & tryitandsee for their replies.

In answer to TicklyT
I have only one mixer tap in the kitchen (Franke Triflow) which is mains cold water fed. Presumably, if this was the cause then this mixer tap would have to be leaking across the cold and hot water circuits within the tap to cause this problem, is this correct? This tap does not exhibit any leak at all into the sink.

the CWST is approx 60 cm above the central heating F&E tank.
No hot & cold feed washing machine, cold feed only.


In answer to tryitandsee
No only, the one mixer tap as described above which has been installed for 7-8 years.

Last night, I turned off the CW feed to the cylinder, turned off the mains supply tap to the CW feed tank, turned off the boiler and placed a container under the CW tank vent pipe. This morning there was no water in the vent pipe container and the water level in the tank did not increase overnight, as it should be. Additionally I checked the central heating F&E tank, this was unchanged, i.e. did not change from its normal level.

Tonight I will set the heating (HW only) to start normally (On at 05:00 am off at 09:00 am). I will close OFF the CW feed to the cylinder but turn ON the mains feed to the CW feed to the cylinder tank and leave the container under the vent pipe.

Garry
 
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Starting to become difficult to follow.

As I see it, water is back flowing through the cold water feed to the cylinder.

This would be a split/leak in the indirect cylinder coil. However you are saying that the small F & E tank is lower (60cm) than the hot water header tank. The laws of gravity must then rule this out. However it would fill the header tank if the pump some how operated independently. Unlikely as the pump should only operate with the boiler........which you say is switched off!

Are you sure the water level in the F&E tank is lower than the hot water header tank bottom fill pipe? As the levels would try and balance each other (like an improvised water level).

Interesting, keep posting. Like to know the reason.
 
To clarify the situation.
I have established that the surplus water entering the hot water tank is entering via the feed pipe.
I have checked the following.
• Ball cock shuts off perfectly.
• No water entering the hot water tank via the hot water vent/overflow pipe.
• Running the gas boiler has no effect i.e. water enters the tank when boiler is allowed to heat the water AND when I turn the boiler off thus no hot water heating taking place.
• Water level rises beyond ball cock shut off point during the day, although normal domestic use of the hot water prevents any overflow.
• No additional water is entering the central heating F&E tank, this has remained at a constant correct level.


Additional information.
• I have one mains fed mixer tap in the kitchen which does not exhibit any tendency to leak.
• I have a mixer tap in the bath but both hot and cold supplies are gravity fed.
• I have a separate pumped shower, but both hot and cold supplies are gravity fed.
• I do not have any machines connected to both hot and cold water feeds, all ours are single cold water mains fed appliances.
• No immersion heater has been switched on.
• Three tanks are located in the loft, one is for the gravity fed cold water (Upstairs bath, shower, toilet etc) one tank for the house hot water (feeds the hot water cylinder) and a smaller feed/expansion header tank for the central heating. The central heating F&E tank is located 60 cm directly below the hot water feed tank (The topmost edge of the CHF&E tank is some 45-50 cm below the bottom of the hot water feed tank).


Garry
 
god55 said:
To clarify the situation.......
Three tanks are located in the loft, one is for the gravity fed cold water (Upstairs bath, shower, toilet etc) one tank for the house hot water (feeds the hot water cylinder).....

Garry

Two independent cold water storage tanks is a little unusual, although two tanks side by side and interlinked, so they behave as a single tank is not uncommon. it is then usual practise to take feeds to both hot and gravity cold from the tank furthest from the single ballcock supplying both tanks to prevent stagnation.

Is the water level in both the 'hot and the 'cold' storage tanks exactly the same? if there is any difference, then maybe your shower and bath mixer should be added to the list of suspects.
 
Is the vent pipe blocked with sludge, thereby expansion/venting is taking place in the hot water feed pipe.
 
god55 said:
I have established that the surplus water entering the hot water tank is entering via the feed pipe.
.
.
.
• Water level rises beyond ball cock shut off point during the day, although normal domestic use of the hot water prevents any overflow.
.
.
.
• I have one mains fed mixer tap in the kitchen which does not exhibit any tendency to leak.
Install an isolating valve on the supply to the kitchen cold tap, then, making no other changes, while the symptom is evident, shut off this isolating valve.

If the kitchen cold mixer is the cause, then the symptom will stop, and restart when you re-open the valve.
 
Install an isolating valve on the supply to the kitchen cold tap, then, making no other changes, while the symptom is evident, shut off this isolating valve.

Thanks Softus, that’s certainly worth a try.

Is the water level in both the 'hot and the 'cold' storage tanks exactly the same? if there is any difference, then maybe your shower and bath mixer should be added to the list of suspects.
I will also look into TicklyT suggestion.
Although the two tanks (Cold water and hot water supply) are both at the same height and identical in size I will check that the level of the cold water is not over filling significantly. If it is overfilling (It’s not overflowing), I will reduce this to its correct level, then shut off the mains supply overnight and check the level in the hot tank in the morning.

Is the vent pipe blocked with sludge, thereby expansion/venting is taking place in the hot water feed pipe.
Thanks tryitandsee
Is there a way of checking this? The end of the pipe is clean, I have inserted a wire for perhaps the first 50 cm without any obstruction.

I am really appreciating all your time and help with this problem.

Garry
 
I'm sure we are all confusing you with all out suggestions.

It must be a small amount of water entering the storage tank if by running hot water stops it overflowing for some time.

Attach hose to tank end of vent pipe and back flow water to clear any blockage.

The other thing can be when the pump causes back flows up the expansion/vent pipe due to badly designed pipe circuits. You haven't increased the pump speed recently by any chance! ? This back flow will get worse (if it's going to happen) when the central heating circuit is closed for the summer.
 
god55 said:
Is the vent pipe blocked with sludge, thereby expansion/venting is taking place in the hot water feed pipe.
Thanks tryitandsee
Er, I think tryitandsee is getting confused with the primary circuit, which can suffer from sludge. The DHW vent, whilst it might get blocked with scale, never seems to.

Is there a way of checking this?
Yes.

Shut off the cold feed to the cylinder, and run a hot tap. If water comes out normal normally then tails off to nothing (or to a drip) at a linear rate, then your vent is clear.
 
Shut off the cold feed to the cylinder, and run a hot tap. If water comes out normal normally then tails off to nothing (or to a drip) at a linear rate, then your vent is clear.
Thanks, I tried this and the hot water stops running within 30 second approx. as predicted.

Assuming of course your valve actually works
Yes it works, I am shutting this valve off every night before going to bed, it’s the means that I am using to stop overflow during the night.

I will take a look at the COLD water supply tank today as suggested by "tryitandsee"
I will also buy an isolating valve for the kitchen mixer tap and insall it to eliminate this tap.

Does anyone have any experience with the SureStop water switches, both the remote and direct, are they reliable and worth fitting?


Garry
 

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