No hot water when heating goes off

1580Steve · 22-04-2009 01:59PM #1

Hi all, I know nothing about plumbing but have recently bought a house and i think the previous owner was a bit of a handy man. Anyway my problem is when I put the gas heating on, all the rads heat up no problem, if you run the hot water it's hot, not boiling, you couldn't take a bath with it, not that hot. When the heating goes off, after maybe 30-40mins if you run the hot taps, the water is cold again. I have tried to look for a throttle valve on the cyclinder but there is none as I think the previous owner moved the cylinder, also the feed into and out of the coil in cylinder gets hot but the whole cylinder never heats up, only the very top. I have tried closing all rads and runnling heating but it doesn't make much of a difference.

Any ideas about this please?

10-10-20 · 22-04-2009 08:18PM

Sounds like the system isn't balanced or setup correctly.
What happens if you turn off all of the room stats (to a low temperature) and run te heating? Does hot water flow into the hot water tank? I suspect not.

Are there any controllers or electrical valves that you can see in the hotpress or on the piping near the boiler?
If so, can you force them open (using the manual level on the valve) and see whether the hot water flows to the tank?

1580Steve · 24-04-2009 02:15PM

I have tried turning all the rads off and running heating but no change. The boiler is a back boiler and I'm not sure about controlls around the pump and don't really want to go messing with them. In the hot press where the cylinder is there are no electrical valves as it is a very old system. Would replacing the cylinder and getting it re-plumbed sort the problem?? I would love to have a bath!!!

10-10-20 · 24-04-2009 03:50PM

It sounds to me like a standard back-boiler system with a difference.
You could consult a plummer, you may be able to get away with installing a bypass pipe which delivers the hot water to the cistern directly, instead of seemingly running it through the rads.

1580Steve · 24-04-2009 04:38PM

I have a plumber friend coming to have a look after the weekend, strange thing is that even with the heating on for a few hours the hot water is only hot and hot scalding and still won't stay hot after heating goes off.

10-10-20 · 24-04-2009 04:40PM

You'll get this if the tank and the rads are on the same circuit.
The warm water leaves the tank and moves to the rads under the pressure of gravity.

1580Steve · 24-04-2009 05:22PM

So is it a big job to get this sorted? The previous owners never had an electrical shower so surely must have been able to have a hot bath!

10-10-20 · 24-04-2009 05:23PM

That's a question for the plummer...
It could be a 15 minute fix, or a 1 month nightmare...

Keep us posted.

1580Steve · 24-04-2009 05:33PM

I know he mentioned there could be a high point in the coil in the cylinder and it might be a case of changing the cylinder, I would prefer to have a better insulated one anyway because I'm trying to be more energy efficiant in the house!!

1580Steve · 24-03-2010 05:35PM

Just to close this thread, I eventually narrowed it down that the pipe that fed the hot tap in the kitchen extension was leaking when it was hot, no visible leaks or damp as it is under the ground somewhere so I ran a new feed to the tap from the cylinder and hey presto eveything is working perfect!!!! Yipee!

No hot water when heating goes off

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