I've had three heating engineers out whenever this issue presents under my emergency homecare package and not one of them has been able to adequately resolve a recurring issue and it's starting to wear thin so I wonder if the collective has any thoughts because I've drawn nothing but blanks.
We have a Glow Worm Flexicom 18sx condensing boiler, a Drayton Lifestyle programmer for hot water and upstairs central heating and the downstairs underfloor is controlled by Heatmiser programmable thermostats across 4 zones. I also have a solar thermal water system on the roof connected to the water tank. The heating works perfectly every time we ask it to. The hot water works all the time within it's timer settings UNLESS the tank has drained itself of hot water, which means that after a bath and a heavy washing up session have exhausted the tank, trying to manually advance the hot water or set to always on results in nothing happening at the boiler, or the diverter valve if the heating is already on. If you reset the thermostat on the tank, the diverter will spin up and send a pulse of hot water to the tank if the central heating is on and then stop, even if the programmer is set to on rather than timed. Nothing I did last night would allow hot water to be pushed to the tank, boiler reset/thermostat reset/triggering all the heating zones etc. The diverter was replaced the first call out, the thermostat identifed as potentially faulty second call out so I was shown how to reset it and the third call out was for a replacement expansion vessel on the boiler but when asked about the hot water they were also at a loss to explain. I don't actually know how hot water was restored the first two times by the engineers.
Here's where it gets stupid - this all happened again last night, and I gave up and went to bed destined for a cold shower this morning. I woke up and the boiler had triggered the heating upstairs correctly at half six, and had also heated the hot water tank from it's overnight low of 17c (my solar thermal water system has two probes so I can see what the tank temp is at two places) back up to where it should have been at 65c. I have absolutely no way of accounting for why this is happening. The hot water period between 0730 and 900 has now finished this morning, and if I go and advance the hot water (having fed two showers and it reading 57c) the boiler kicks in as if nothing happened and starts delivering hot water to the tank.
Now, we mostly get round this by just not using all the hot water, but this is pretty unsustainable going forward because we don't have any backup electric shower or a working immersion (I press the switch and nothing happens?), so when we lose hot water on demand we seem to just have to wait for the next timed slot to kick in. I haven't tried removing the time slots from the programmer to confirm yet, but you'd have thought it would just be as simple as pressing the advance or setting to always on and it'd just...work?
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