Horstmann electronic 7 only heating water using boost not timed off peak....

[heather76]

The unit only heats water using the programmed boost and when pressed in the 1 2 or Cont boost function. I have checked the off-peak time which is set to 2.30-7.30 am - this is when the Horstmann should do its thing...? But it's not heating the water so only the top cylinder works on boost, the bottom cylinder nothing.
An engineer did check the bottom cylinder which hadn't tripped and said there was power there.
Could this be a problem with the unit or element in the cylinder?

 

[Avo Mk8]

The unit only heats water using the programmed boost and when pressed in the 1 2 or Cont boost function. I have checked the off-peak time which is set to 2.30-7.30 am - this is when the Horstmann should do its thing...? But it's not heating the water so only the top cylinder works on boost, the bottom cylinder nothing.
An engineer did check the bottom cylinder which hadn't tripped and said there was power there.
Could this be a problem with the unit or element in the cylinder?

It's likely to be the immersion heater element at the bottom, if power was available there.
It's a pity the engineer did not go on to measure the resistance of that element, because that could have told him (and you) if it was definitely defective.
There's likely to be a safety cutout in the head of the immersion heater (operates if it gets too hot), and if that has tripped, it's possible it requires resetting, though these days most of them self-reset.

All in all I think you need a tradesman to investigate, and probably change the immersion heater.
An electrician using test equipment will be able to definitively say if the immersion requires replacement, but in my limited experience, because it requires draining all the hot water from the cylinder, and sometimes the immersion is difficult to take out, not all electricians are prepared to do the "plumbing" to change it!
On the other hand a plumber will happily change it, but we'll never know if it was a thermostat or safety cutout problem!
If you investigate under the cover of the immersion, obviously make sure the power is off at the timer and the consumer unit(s).

 

[brianmoooore]

if that has tripped, it's possible it requires resetting, though these days most of them self-reset.

@Avo Mk8 . Are you sure about that? I thought it was a requirement that they do NOT auto reset, since the only reason they should have tripped is as a result of a problem with the main 'stat.
The new ones I have on the shelf definitely need to be manually reset.

 

[Avo Mk8]

@Avo Mk8 . Are you sure about that? I thought it was a requirement that they do NOT auto reset, since the only reason they should have tripped is as a result of a problem with the main 'stat.
The new ones I have on the shelf definitely need to be manually reset.

You are absolutely correct. Don't know what I was thinking, in fact I clearly wasn't thinking at all

So Heather76, if you do find the over temp trip has activated, and the immersion does heat up once it's reset, it nevertheless suggests there is something wrong (eg with the thermostat) meaning replacement parts will be needed.
Apologies for the mis-information, and thank you brianmoooore for the correction.

 

[littlespark]

isolate the circuit before poking around looking for the overheat reset.

Just saying

 

[brianmoooore]

isolate the circuit before poking around looking for the overheat reset.

Just saying

Most definitely! The ones I fit have a short reset button cleverly placed between two bare live terminals which are about 20mm apart.

 

[brianmoooore]

the only reason they should have tripped is as a result of a problem with the main 'stat.

Having said that, in cases where the water is also heated by a solid fuel appliance, such as a wood burner or Aga, they can be tripped on occasion if the water gets way above the temperature it's heated to by the immersion heater.

 

[heather76]

It's likely to be the immersion heater element at the bottom, if power was available there.
It's a pity the engineer did not go on to measure the resistance of that element, because that could have told him (and you) if it was definitely defective.
There's likely to be a safety cutout in the head of the immersion heater (operates if it gets too hot), and if that has tripped, it's possible it requires resetting, though these days most of them self-reset.

All in all I think you need a tradesman to investigate, and probably change the immersion heater.
An electrician using test equipment will be able to definitively say if the immersion requires replacement, but in my limited experience, because it requires draining all the hot water from the cylinder, and sometimes the immersion is difficult to take out, not all electricians are prepared to do the "plumbing" to change it!
On the other hand a plumber will happily change it, but we'll never know if it was a thermostat or safety cutout problem!
If you investigate under the cover of the immersion, obviously make sure the power is off at the timer and the consumer unit(s).

Thanks for this, very helpful.