How would you use electric immersion heater on boiler fed hot water cylinder?

[ElCI]

Hi all

This is related to another post I have about RCD issues. I've moved into a house that has a roughly 30 year old heating system. This has a hit water cylinder that's fed)heated by the boiler but also has a 3kw immersion heater fitted at bottom end of the cylinder. I can't work out how/when the immersion heater would be used practically. I understand it can be a backup in event if boiler not working but how do you choose to turn it on? The controller has a "boost" mode, would this be how it's used?

Essentially I'm just looking to confirm that it's ok to isolate the water heater at the consumer unit without affecting hot water but I'm also generally curious as to how it works

 

[Rodders53]

That switch on wall feeds 240V electric to the immersion via a thermostat built in behind the cover cap to control the water temperature.

Switch that OFF asap!!

If the MCB in the consumer unit is off then less important. But often better/easier to use the switch in the airing cupboard in emergency for hot water than accessing the Consumer Unit. (For me, that means going outside to the attached garage!)

The gas boiler controller boost function is just to make the gas boiler operate for a time, usually one hour, outside of the scheduled on times for CH or HW.

 

[ElCI]

That switch on wall feeds 240V electric to the immersion via a thermostat built in behind the cover cap to control the water temperature.

Switch that OFF asap!!

If the MCB in the consumer unit is off then less important. But often better/easier to use the switch in the airing cupboard in emergency for hot water than accessing the Consumer Unit. (For me, that means going outside to the attached garage!)

The gas boiler controller boost function is just to make the gas boiler operate for a time, usually one hour, outside of the scheduled on times for CH or HW.

Hi, so I've only just isolated at CU today. I moved in almost 2 weeks ago, does this mean that the 3kw element has been running constantly since then?? I have an Octopus energy smart meter and it's not looked too bad for consumption but that's very worrying if being run constantly, any idea how much that would be costing (in panicking a bit here that I could've run up a massive bill already)

 

[Rodders53]

Having read your other CU RCD post...

The switch will be DP and isolate a Neutral fault in the flex and/or the immersion heater if the thermostat calls for heat. So turn that OFF.

I expect the electric immersion may have failed? But yes if it's been on and the immersion stat has called for heat it will have been drawing power.

If the boiler has heated up to hotter than the immersion is set it may not have used Too much electric?

 

[ElCI]

Having read your other CU RCD post...

The switch will be DP and isolate a Neutral fault in the flex and/or the immersion heater if the thermostat calls for heat. So turn that OFF.

I expect the electric immersion may have failed? But yes if it's been on and the immersion stat has called for heat it will have been drawing power.

If the boiler has heated up to hotter than the immersion is set it may not have used Too much electric?

I have this (marked "water heater") under the boiler, does this mean there's basically 2 isolators in series for the immersion heater? (One in boiler cupboard and one in cylinder cupboard)?

 

[Rodders53]

No idea. It would need some metering and/or cable route tracing to know!

Just cos the isolator with neon says 'water heater' it could supply anything, anywhere. It would be strange to have two isolators in series but then some installers and house owners do strange things!