Help, Central Heating Hot Water Problem

Have to say there are folk here giving advise who should be on TV, on comedy programmes

OP, you have two motorised valves and most likely two thermostats to operate respective motorised valves

When you make a demand, say HW on the programmer, that zone motorised valve opens. If the synchronous motor is faulty, dead, cuffed, gone to heaven, dead as a dodo etc, the valve will not open and boiler and pump will not run so forget taking things apart if boiler fires up when you select HW and lower pipe at the cylinder heats up

The hot water entering the cylinder coil looses heat to body of water you are trying to heat. This primary flow, now cooler returns to the boiler to be reheated to continue the cycle until thermostat on the cylinder or your timer stops the cycle

Hint. Leave HW switched off, fire CH, run for say 30 minutes to get the system hot. Now switch CH off, go to the cylinder and locate the two pipes connected to the cylinder and get someone to switch HW only on. One pipe will get hot almost immediately, other a few seconds later but not as hot. If the temperature difference excessive, offer a magnet to these pipes and look for signs of blockage where the magnet will stick to sludge within

You have an old system, no doubt fitted by an old duffer who knew how to do a good job so plumbing should not be an issue, only age related problems

Wish you good luck in your search

DP said:

Have to say there are folk here giving advise who should be on TV, on comedy programmes

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Great post, made me laugh so thanks very much. Your description is as I understand the system. Anyhow I took a look at both MV valves, when the CH is selected one motor opens, the other closes - I saw this by removing the actuator heads. The physical valves also BOTH operate normally - the one for the water was maybe a little stiff but nothing to write home about.

Here's the thing though, the tank still doesn't get hot! When HW is selected the valves operate, I can feel the pump running and I hear the boiler fire. Shortly afterwards the boiler shuts down and the pipes near the MV are read hot (the ones at the tank are cold)

As an experiment I manually opened the HW MV and turned the CH on. The radiators got hot and the tanks STILL stayed cold. I am beginning to think there's a block to the tank like you say. I'll try and find a magnet. Can you confirm my logic and is there anything else I can try?
Thanks
DD

PMN: Just found a magnet, none of the pipes I can easily access appear magnetic. Admittedly that's not many.

What can I say I completly missed the cylinder stat so thought it was gravity system.

picasso said:

What can I say I completly missed the cylinder stat so thought it was gravity system.

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Do you suspect that? Why would the boiler fire at all if it wasn't working?

It could be a pump problem. When the pump is running, put a screwdriver tip against it and listen. If it's a high speed sound, the pump's ok, if it's a low speed noise, then that could be the issue. Is the cylinder miles away from the pump?

denzildexter said:

picasso said:

What can I say I completly missed the cylinder stat so thought it was gravity system.

Click to expand...

Do you suspect that? Why would the boiler fire at all if it wasn't working?

Click to expand...

Sorry I was replying to the poster before you (dp)

Bitzerdisandat said:

It could be a pump problem. When the pump is running, put a screwdriver tip against it and listen. If it's a high speed sound, the pump's ok, if it's a low speed noise, then that could be the issue. Is the cylinder miles away from the pump?

Click to expand...

The cylinder is on the first floor pretty much directly above the pump. I would say 3m to 4m at most. Not sure about the pump sound, it sounds (and feels) the same when the CH is on as it does with HW. No problem getting the rads hot.

Hi Danzil, ok, this is a tricky one!
How quick do all the rads get hot when the heating is switched on?
I still think it's all down to that motorised valve. It's as if the valve has broken inside. Sorry, but I think it's a drain down and inspect that valve. If it's broke, just get one from the plumbers merchants. If needed, ask for a 22mm, 2 port m v.

Thanks to all that have helped so far. I have given up and called in a pro as I don't fancy flooding the house trying to drain down the system When it's fixed I'll let you know what the actual problem was.
Thanks again,
DD.

Ok my friend. i bet it's the hot water m v. It's probably broken or jammed. If the heating water is dirty, ask him to fit a magnaclean. Worth every penny as they stop things jamming with sludge / iron oxide particles.