Horstmann Water heater controller for Economy 7

PCD1962 · Sep 17, 2023

Yesterday moved my Mum into her new bungalow. The Hortsmann had been off for a few months I suspect. The boost worked, but nothing happened overnight on economy 7 even though I set the timer dial correctlt etc, so no hot water this morning. I can't see anywhere in the threads on here whether once the battery back up is completely dead, whether this will start working ok again once it's recharged? Or is there some resetting needed?

brianmoooore · Sep 17, 2023

Like any rechargeable battery, it will recharge if it's in good condition, otherwise it will not.
Is the dial maintaining the correct time? If so, the battery is not the problem and is more likely to be with the immersion heater itself. If set up as intended, the boost control will use a different immersion element than that used by the timed heating.

PCD1962 · Sep 17, 2023

Thanks Brian - yes the dial is maintaining the correct time. So from what you've said, battery ruled out.
The boost works as I said (using the higher of the 2 elements I think?), so looking like the timed heating immersion heater.
Very helpful, thanks again

brianmoooore · Sep 17, 2023

All that's been established so far is that the problem is nothing to do with the battery.
Have a close look at the front of the controller, just outside the dial, just below half way down on the right hand side. The microswitch that switches the power for the timer is just behind here, and if it overheats and fails will cause some distortion and discolouring of the plastic front.
Could be as simple as each immersion heater has a local isolator switch, and the one for the timed immersion is switched off.
Unless the immersions are really old, they will have some kind of overheat protection built into them, in case the thermostat fails in the 'on' position. These occasionally trip for no apparent reason, so it could be just this needs resetting.
The types vary, but the cover over the immersion head will need to be removed to check. MAKE SURE THE POWER IS OFF. If the single nut holding the cover is loose or even missing, it's a good indication that this safety cut out regularly trips and it, or the main 'stat, is probably faulty.