No hot water but do have central heating

26 Mar 2021
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United Kingdom
Hi there

When I switched on my hot water at the controls today, I noticed that I couldn't hear the 'normal' noises it would make once it comes on and the hot water cylinder isn't getting hot.

I have tested the central heating and it works fine.

I have a plumber doing work on renovation at the moment. He's removed some radiators and had to bung the cold water tank to cut radiator pipes no longer needed. As a result, there seems to be some air trapped in the system and one of radiators doesn't work with the inlet flow pipe cold.

Could the hot water issue be linked to these other issues eg trapped air?

Are there any tests I could do to try and identify the cause of the issue?

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Trapped air is certainly a possibility, but several other things may be the cause. Why not speak to the plumber who is doing the work ?
If you have an immersion heater fitted in the cylinder you could use that temporarily.
Thanks both. The work is through a builder so I have said that the plumber needs to look at the issue when he is next back

The initial response from builder is that the hot water issue is unrelated and it is a boiler issue so I want to make sure I can rebut this as I don't want him to try and charge extra.

This thread seemed to suggest an air lock could be the cause and to loosen the compression valves for the boiler pipes flowing to the hot water tank to see if air comes out. Do you think that's something to try?


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Put the CH and HW both on, then manually open the HW zone valve and latch it open and see if the HW heats up
Before you do too much, make sure there are no bungs or stops or whatever in the f & e tank for the primary circuit and the header tank for the hot water. That pic suggests a heat only or system boiler, your builder is assuming you have a combi.
Thanks all.

Tank isn't bunged anymore.

Yes, I have a heat only boiler - definitely not a combi! I think my builder doesn't want to ask the plumber now in case he wants more money from the builder!

ianmcd - I manually opened the Honeywell port for the hot water and have put the central heating and hot water on. Pipe into the hot water tank is now hot so this works as a temporary fix.

If I only switch on the hot water with the HW port manually open, the pipes don't seem to heat up ie boiler not heating up.

Any ideas why? Again, I'm looking for reasons why this issue could have been caused by recent plumbing works. There's still a new radiator and sanitary waste to be hung so the plumber definitely should be back!


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Most likely an electrical issue (either cable to 2 port valve has failed/been disconnected or valve motor has died).
Run with the bodge for now, talk to the plumber when he shows up. Or get your multimeter out & check for power at the 2 port valve
Thanks oldbutnotdead.

When I manually open the CH port valve when CH switched on, it moves with no resistance.

When I manually open the HW port valve when HW switched on, it moves with resistance.

I assume this backs up your point re likely an electrical issue?

Possibly a slightly naive question. If the HW valve is not opening when HW switched on, is this why the boiler doesn't come on when HW switched on?
Just to add that for the last few weeks, the hot water from the shower mixer has not been as hot as it should be (hot water cylinder and cold water tank mixer). I assume it is likely to be linked to this issue in some way?
There should be a bit of resistance from the spring. Well worth popping the lid off (beware live parts inside, isolate first) and having a look.
The manual lever doesn't operate the microswitch in the mech (which is what signals the boiler).
Also worth checking the cylinder thermostat is still in position & set to a sensible value (maybe plumber has knocked it down to 20 while doing stuff)
The motorised valve sends voltage to the boiler to fire it up. manually opening the valve will enable water to flow to the cylinder ,but will not fire up the boiler.
When all is working as it should ,the motor in the valve does two things ,it opens the water pathway and it triggers a microswitch that switches the boiler on.
ianmcd - I manually opened the Honeywell port for the hot water and have put the central heating and hot water on. Pipe into the hot water tank is now hot so this works as a temporary fix.
yes eithercoincidentally the motor in the HW zone valve has failed at the same time as the building work is being done, or the wiring has been altered in some way and the valve is not getting power, either way easy fix so wouldnt worry too much, you know now how to get HW by manually opening the valve and putting the heating on at the same time, talk to the builder and politely explain what has happened and ask the plumber to sort it

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