Plumbing Problem: No hot water getting to hot water cylinder

eggerb

Any advice much appreciated!

I have a gas boiler which heats my rads and hot water. When I turn the gas boiler on, I previously had hot water from the taps and hot rads. Now, I just have hot rads unless I turn on the immersion in which case I get hot water as well. Therefore, the problem seems to be that the hot water from the boiler isn't getting to the cylinder. (When I heat the water in the cylinder via the immersion, I have no problem!)

Working on the picture below,



the two pipes at the top are (I think ) hot out. These are cold.

The pipe at the bottom (with a drain valve), I'm not too sure about. The two pipes in the middle are hot in (I think). They are both very hot right up to the cylinder (pass the valves) when the gas is on but it is as if the water doesn't get into the cylinder. I'm not exactly sure why there is to hots in (or two outs) but they seem to be joined by a pipe (not sure if the valve should be open or closed) and one of them has a thermostat (again not sure the purpose of this).

Any thoughts much appreciated.

ART6

The cylinder will have four pipes. One is from the header tank in the roof supplying cold water, and one is hot water out of the tank to taps. Then there are two pipes to the coil that is inside the tank, and that works from your boiler. The boiler circulates hot water through the coil inside the cylinder and through your radiators, and it is a closed system -- ie it keeps going round and round. The picture you showed suggests that the two pipes with a connection and a valve between them are the connections to the coil, so the valve should be closed. I am not sure what purpose the thermostatic valve on the upper pipe serves, but if it's stuck it could be the cause of your problem, and they do have a habit of sticking.

From what you describe the flow and return on the cylinder are OK, since if they were not then the immerser would turn off without giving you hot water to your taps.

So, solution. Open the thermostatic valve as far as it will go and make sure the bypass valve is closed. If the boiler still doesn't give you hot water to your taps (give it an hour or two with the immerser turned off) then try a few gentle taps with a small hammer on the body of the thermostatic valve. As we engineers say, if that doesn't work, get a bigger hammer.:D

JamesM

The thermostatic valve and the bottom red valve should be open. As ART6 says, there is a pin in those thermostatic valves that sticks closed - if you take off the head, you can sometimes free the pin. The other problem could be, not enough water in the heating system. The cylinder is probably the highest point in the system, so if there is not enough water, the air gathers in the top of the coil.
Jim.
Edit: Close the bottom red valve and open the middle red one. If the middle pipe heats, then your problem is that the thermostatic valve is stuck closed.

eggerb

Many thanks for the replies Art6 and JamesM. This is what I have done:

Took thermostatic valve off altogether and made sure the pin was up. Water is definitely getting past the thermostatic valve;
I closed the valve on the connection pipe between the flow in and the return out;
I made sure the bottom valve is open on the return.

Both the the flow in and the return out are piping hot.

Two hours later the water from the hot taps seems to be getting hot! Its not really that hot though - nothing like as hot as the pipes going into the cylinder. Normally, a half an hour gives us enough water for two longish hot showers. At this rate, I'd be a thousand times better off using the immersion. I wonder has my problem anything to do with me not using the gas boiler for two weeks as I was on hols?

Is there anyway for me to check and solve the problem of not enough water in the heating system? There does seem to be a pipe extending about 4 inches higher than the flow in with a fitting that looks like it could be "bled" (if this is the term). This is piping hot to the top too though.

Two hours and a bit more and the water is a bit hotter. Maybe I'm just a bit impatient? But two hours to heat some water isn't a runner!

Cheers again for the replies.

JamesM

Glad that it's working. If the system has been off for a while the whole cylinder will take longer to heat the water from cold. Maybe check the pin again - push it down a few times and make sure that it comes up fully. If the return out at the bottom, is piping hot, the flow is good through the cylinder.
Jim.

ART6

Another possibility is that if you live in a hard water area the coils inside the cylinder are simply scaled up. If so you could use a descaling solution but you would have to flush the hot water system very thoroughly afterwards. As Jim said, it will take more than two hours to heat the cylinder from cold using just the water circuit since it it not as efficient as the immerser.