Thanks for the updates from folks, just spoken to plumber and will get the work done and will see how it goes.
I have been manually (just switching on elec heating element) trying to use our solar to heat the water tank but that does not seem to have stopped the boiler from coming on at 7pm when the tank should be at temp, so by getting this done I can see what the actual water temp is and if the heating element works.
For the record I still get "comms errors" from the hot water sensor. Nothing I do will fix it. I have just learnt to live with it because I have better things to do with my time.
From sniffing wireless traffic it seems to be caused by a combination of the CS92A not sending temperature updates frequently enough when outside the differential band (and/or when the temperature is steady) combined with the Evotouch controller not receiving transmissions from CS92A's reliably when a 3rd party device is receiving the "missing" transmissions ok.
Either a problem with the radio receiver (insensitive and/or timing errors affecting decoding) and/or a firmware bug.
Defective by design unfortunately so unless Honeywell release new hardware revisions the hot water sensor will never be completely reliable.
When I eventually replace my ancient boiler I'll probably go with a combi (as we have an electric shower and only two hot taps) and that will solve the problem once and for all!
You may not get the confirmation you need. Having just replaced my old cylinder with an unvented one (Joules), I have inserted temperature probe into the thermostat pocket. Modern cylinders are very good at not mixing hot and cold water. The first thing I noticed is that even if the sensor is reading a fairly low temperature, the water at the top of the tank is still very hot. Nothing unexpected here, except that you cannot rely on the temperature probe to let you know how much hot water you have in the tank.
Secondly, I have solar panels, and divert to the immersion automatically when I have more generation than consumption. When this is happening, I see no rise in the temperature of the water where the probe is. (The immersion is higher in the cylinder than the stat pocket) I can put 4kWh into the tank, and the temperature does not rise at all (but the water around and above the immersion is heated.)
I've never had any issues with my own CS92A, only when it needs new batteries. Other than that it's been perfect. I get the Comms error when the batteries are low, change em and it's good for another 18/24 months.
Hi that is really useful to know and could explain something I have seen.
Even when I have had the heating element turned on during the day the 6pm boiler fire up has sometimes still happened when I would expect it not to.
That could be explained by the position of the two sensors. Heating element at top and boiler at the bottom (ish)
I will perhaps know more when I get the EvoHome kit installed but plumber has yet to quote, I have an electrician coming around tonight and perhaps I will ask him if he would do the electric side of things as it really does not need a plumber.
Trying to get Trades folk today is a mare....