> 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!