Hot water entering cold tank

Hey David, Sounds like you have more then one problem. The first most pressing problem is the leak you have in your cold water feed. You must localize it by turning off the water to the house at the main house, (not the meter) shut off. If the little pointer is still turning in the meter after you shut off the house than your leak is in the underground supply to the house. Since you have checked the Hot water heater temperture and pressure valve to make sure it's not faulty and you have no water coming out of the walls and the cold water feed checks out then the leak may be under a cement floor. Are you on a slab or do you have a basement. Please explain what the function of a "cold tank" is and how it fits into your system also what is a diaphragm valve that you changed? Ball valve, globe valve, temperture and pressure valve or a check valve. Get back to me and I'll answer ASAP. Cheers, Tom

Thank you Speedball for trying to solve my problem.

When I turn off the water at the house, there is NO water running through the meter. Therefore I know that there is no leak between the meter and the house. However, with the mains water switched on, the boiler switched off and no water being used at all, something is running, because the meter is going round. There are some pipes running to an extension at the rear of the house, which must run underground. If there is a leak, then it must be in the underground section. It cannot be anywhere else in the house or I would see the water!

The cold tank is in the attic/loft of the house. It provides about 40 gallons of cold water storage. It feeds cold water to the hot water tank, which is situated on the floor below. Since the hot water is gravity fed, it supplies a low pressure for the hot water delivery. The diaphragm valve is just a type of ball valve on the tank. I think the other type is called a Portsmouth valve.

There is also another (much smaller) cold water tank which only feeds the water which flows through the radiator pipes. I don't think that there is any problem with this.

Given time, I can find an underground leak with the right detection equipment or just breaking out the concrete! What I don't understand is how warm/hot water can be feeding back into the cold tank!

I hope that this makes it clearer
David

Does the boiler have a coil in it that heats water to supply the hot water to the faucets in the house? If that coil had a leak, cold water would feed into the boiler, be heated and flow up to the cold water tank making it over flow. If the leak wasn't too big, you would still have hot water at the faucets, perhaps with the pressure down a little. This is dangerous providing a cross connection between your drinking water and the boiler water.

Keep posting back with more information. I haven't seen a problem yet that Tom and I didn't figure out. We don't quit.

The best way of describing the hot water system is to point you towards a sketch of a typical system. I have, therefore, attached a file which shows the way the typical UK system works. I hope that make its clearer. The plumber checked the ventpipe and said it was clear.

David

Still !

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I think Labman went right to the heart of your problem when he focused on the immersed heating coil. If there were a leak in the coil that would give you a direct crossconnection between hot and cold. Labman should be the last word on this as I'm a Florida plumber and we heat with reverse air or electric heat strips. Labman's the expert on home heating systems on this site. He's much more versatile then I so pay attention to him when he offers advice.

(YOU)"There are some pipes running to an extension at the rear of the house, which must run underground. If there is a leak, then it must be in the underground section. It cannot be anywhere else in the house or I would see the water!"
(ME)And I think you're right about your running water leak. While the leak in the coils would permit a cross connection between hot and cold it wouldn't allow the water to run steady through the meter as you have a closed system. One way to check it out before you start to dig would be to install stops on the lines going underground and then close them down. If the meter stops turning you lave localized your leak and until it's repaired and you will have water in your house without shutting off the mains all the time. Sound like a plan?

Your system does not work like I thought. The systems where hot water is heated by the heating system are only things I have only read about. I can not see how the the cold water tank could over flow with hot water unless water is being fed into the water heater at a higher pressure than the water from the cold water tank. Is the heating system steam or hot water? If it is hot water, the circulating pump could force hot water out a leak in the coil and back through the line to the cold water tank. I guess steam could do the same thing if it was high enough pressure.

The heating system boiler must have a water line to replenish it. Check to see if water is flowing into the heating system when the meter is running with no known water usage. If so you have found at least one of the problems.

I agree with Tom about adding valves to shut off the underground lines if you have to break the line to see if it is the problem. They may be handy some other time too. I always use ball valves wherever I can. They are easier to use and leak less, never requiring adjusting the packing.

Usually you can hear or feel if water is running in a line. Perhaps try the old mechanic's trick of holding a screwdriver tip to the line and the end of the handle to your ear.

> I can not see how the the cold water tank could over flow with hot water
> unless water is being fed into the water heater at a higher pressure than
> the water from the cold water tank. Is the heating system steam or hot
> water? If it is hot water, the circulating pump could force hot water out
> a leak in the coil and back through the line to the cold water tank.

No I can't understand why either!
The heating system is hot water.

> The heating system boiler must have a water line to replenish it. Check to
> see if water is flowing into the heating system when the meter is running
> with no known water usage.

Yes, there is a waterline/tank for the boiler. I attach/enclose another sketch which shows the full heating system. It is simplified and doesn't show all the valves. I didn't check to see if water is flowing into the heating system, but I think the plumber did. However, it is worth another check. I will go up into the attic tomorrow morning and check. I know that nothing flows into the main cold tank when the main is off. Before I turn the mains on, I will check to see if the water level is down in the cold water tank for the boiler.

By the way, the cold water tank to the heating is very small (not as sketch) and is only about 2'6" long x 1'3" wide x 1'3" deep. The top of the water in this tank is probably just above the level of the cold water feed to the boiler in the other tank. I will check that as well in the morning.

> I agree with Tom about adding valves to shut off the underground lines
> if you have to break the line to see if it is the problem. They may be
> handy some other time too. I always use ball valves wherever I can.

I agree, I like to have as many valves as possible on my plumbing. It makes life a lot easier and any fitting or line that is playing up can be isolated. Unfortunately, I only moved in three months ago and haven't added any. I have only added them in the past when something has gone wrong - like now!

The only other point that I can add is this. The hot water usually takes some time to come through, since it has to "use up" the cold water in the pipes. However, recently it appears that the hot water is coming through a lot sooner, but this might be my imagination.

Thank you once for continuing to help with my problem. Hopefully, I will have a solution soon!

David still

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Your diagram doesn't not show the circulating pump feeding the domestic hot water loop. I guess it could work by convection, but I would expect it to have a pump. Without such a pump and a leak in the loop, I am not sure what could cause the problem.

Here is an update on my continuing saga! As you suggested, the problem could well lie in the hot water tank! I have found out that it is about 40 years old in a hard water area. There could well be a problem in it. Could limescale cause this problem?

I recorded the following this morning:

9.00
Mains water off.
The water level in CW tank (In attic/loft above first floor) is very low (as would be expected with mains water off).
Heating tank (in loft) looks to be at correct level.
Boiler is on.
9.10
Mains water turned on.
9.25
CW tank is now full and ball valve has stopped more water entering.
No apparent change in Heating tank.
Sign of warm water entering CW tank from bottom (which should be cold water feed to hot tank?) This of course shouldn't be happening!
9.30
Boiler off (on timeswitch)
9.35
Every tap & valve is closed (as far as I know!)
Can hear water entering system at mains tap (on ground floor).
Can hear water entering system in cupboard containing boiler and HW tank (on first floor)
10.00
CW tank on the point of overflowing.
No apparent change in heating tank.
I can hear what appears to be water entering the HW tank (directly from mains!?!)
10.15
Water turned off at mains.

I don't know what mains supply must be going directly into the HW tank?

I don't think that there is a circulating pump feeding the domestic hot water. I think that it feeds by gravity. There is a pump for the central heating. However, I will go through the mass of pipes in the cupboard and try and work out what is doing what.

Thank you for your continuing help.

David still