[Closed] STW plumbers assemble - Hot water problem

When you say 'manually' put it on, do you mean turn on the central heating/ hot water, or, the immersion heater?

What type of heating system?
2 valves, one for heat, one for water?
Or a single valve that does both?

The most usual cause is the valve starting to fail.
Unlikely to be the tank thermostat, they are very reliable.

'manually put on' = manually override +2hrs hot water and heating so boiler fired up and heated radiators and water.

There is a motorised valve and I can hear that whirr when I try to do hot water only so I don't think it's that

Diverter valve first, then timer switch are the things I would be looking at. Maybe the other way round.

If there are 2 2 port valves rather than 1 3 port valve, and you can hear the valve opening for hot water then the micro switch in that valve which tells the boiler to fire up might be broken, so the valve is opening, but not telling the boiler to come on. But when you put the central heating on the valve is open, and the central heating valve is telling the boiler to come on so hot water can flow into the cylinder.

If that makes sense. The valve head can be changed without draining the system normally, depending on the valve

when the motorised valve stops whirring, does the boiler fire up?

If the boiler works correctly on the heating demand then its likely to be the motorised valve end switch not making. quite easy to replace a motorised valve head if thats the issue

How many motorised valves do you have?

*throws hat in the ring*

Faulty microswitch in the DHW valve is my guess. Programmer signals valve to open, which it does, but doesn't trigger the pump to start.

[If Honeywell programmer and >5 years old that'd be my next suspect - the capacitors start to fail]

I had this where I had no hot water unless I put the heating on at the same time. Diverter valve knackered, pretty straightforward job (well, for the plumber the landlord sent round to do it)

Not a plumber but I had a very similar problem and it was the cartridge in the shower bleeding cold water over when turned off.
The tank would heat and get hot, as soon as the boiler went off the water rapidly went cold. This was accompanied by a very slow trickle from the overflow that you couldn't see or hear until clearing the gutter.

‘manually put on’ = manually override +2hrs hot water and heating so boiler fired up and heated radiators and water.

This is the bit that's confusing me. Normally with timers I've had you can boost or manually override the hot water or central heating individually so you say you pressed one button and both the water heated and the CH came on.;

I was thinking that maybe there is something wrong with your zone valve that controls your hot water, so that is why it didn't come on in the morning as it usually would.

Bt then you said you boosted it and both CH and hot water came on.

You can override the hot water zone valve manually to open that means when your timer demands Hot Water it should work. Maybe if you try this and see if hot water is available in the morning then that confirms its the zone valve. but doesn't explain why you got hot water and CH when you manually overrode the system. Worth a try. There should be a lever on the back of the solenoid box somewhere if you feel around. Open the lever and latch it and leave till the morning to see if you have hot water.

Thanks all for responding.

Yes, I over-Rode both CH+HW (poor explanation on my part)

Yes, the boiler does fire after the motor has whirred.

There is just 1 motorised valve.

I'll try to latch it tomorrow.

Thanks.