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carmenm · Jan 23, 2006, 06:10 AM

Hello,
I posted my query here a while back but unfortunately it appears to have been left to fester :confused: (query was hot water from cold water tap). After a couple more visits by a plumber, his view is that the hot water tank is overheating, venting hot water into the cold water tank at the top of the house and this is causing our cold water to run hot. Do you think this is possible ? Do hot water tanks have a thermostat that could overheat ? Could this be caused by an overactive immersion heater that appears to be switched off ? Any thoughts welcome...

speedball1 · Jan 23, 2006, 07:39 AM

Hi Carmenm, Where do you live.
The reason I didn't respond is that I was waiting for a new expert, (a UK plumber ) to pick up on it. Since I'm not familiar with gravity fed systems and he is I figured he would take care of it. You have my apoligies.
Is it your plumbers contention that the water heater, (it is a water heater and not a hot water heating system isn't it?) generates enough steam and energy to lift the water up a story to the cold water holding tank but not enough to trip the T & P, (temperture and pressure) relief valve?
Please explain your term "venting" hot water into the cold water tank. Is there a vent from the water heater up to the cold water tank? Please give me more details about your system. Why do you need a gravity fed water system? Poor street pressure? Your plumbing code calls for it? What's its advantage? I just don't know enough about gravity systems to be of much help but I'm willing to learn. The first thing I would question is why they're needed at all. Regards, Tom

carmenm · Jan 23, 2006, 07:58 AM

Hi Speedball, yes you did pass my query on but Martin has concentrated on my original problem (tepid water in the shower) rather than my overriding problem now which is hot water from hot and cold taps.
I'm in London, and my flat is the bottom 2 floors of a 6 story house that was built 200 years ago. The heating system was put in probably about 50 years ago (although not all of it will be that old). It has a boiler that heats the radiator system and heats the water in a hot water tank. Although the cold water comes into the flat at ground level, it then goes up to a cold tank in the roof which feeds the cold water taps and also goes into the hot water tank.
The hot water tank also has an immersion heater in it (electrical) which can be switched on for short periods to provide hot water if the rest of the system is off.
Our new plumber suggests that this immersion heater has broken and is on constantly. This is causing overheating and in an attempt to cool down, the system vents hot water via a pipe from the hot water tank into the cold water tank. Although I can believe there is an emergency system to offload excess hot water, I think it unlikely the immersion heater is on constantly ith the switch off, so am wondering if there is something else that could make the hot water tank overheat ? Problem is, I'm no expert at plumbing :) and these guys are very expensive and for them to keep coming round means I am also losing my annual holiday :mad:

speedball1 · Jan 23, 2006, 08:41 AM

Why would the heating system vent hot water via a pipe from the hot water tank into the cold water tank instead of venting it outside? Why is there a cross connection between hot water heating and cold water storage at all.
I'm afraid you're going to have to deal with Martin on this. He's familiar with your system and the repairs needed where I would be attempting to redesign it. But I sure wish you good luck in the outcome. Tom

carmenm · Jan 23, 2006, 08:49 AM

OK, thanks for your time !

bjacobs · May 5, 2010, 04:59 AM

Your plumber is probably correct. Gravity feed systems do have a vent discharging to the storage tank. If you also have gravity feed cold water supply this will result in heate water being fed to your cold water pipes. The venting pipe is a safety mechanism and if the system is continually venting your boiler should be fixed asap to stop the venting.

bjacobs · May 5, 2010, 04:59 AM

Your plumber is probably correct. Gravity feed systems do have a vent discharging to the storage tank. If you also have gravity feed cold water supply this will result in heate water being fed to your cold water pipes. The venting pipe is a safety mechanism and if the system is continually venting your boiler should be fixed asap to stop the venting.

hkstroud · May 5, 2010, 05:17 AM

Hello bjacobs,
Welcome to AMHD. You have to check the date of postings. This one is 4 years old. Hopefully its been resolved.