Having a short circuit would cause the output current to increase to a high level, hence the Immersun unit shuts down the output to protect both the unit and the external circuitry. The cause could be a short circuit within the wiring or the immersion heater, or possibly within the Immersun unit itself.

If you have a isolation switch between the Immersun unit and the immersion heater then switch this off and see if the fault clears. This would indicate that the fault is at the immersion heater or the wiring connected to it.

If the fault is still present then switch off the power supply to the Immersun unit and disconnect the output cabling. Switch the power back on to the Immersun unit and if the fault is cleared then the short circuit is on the wiring from the Immersun unit to the isolation switch, or the isolation switch itself.

If the fault is still present then the problem is within the Immersun unit.

@derek-m, I left the unit off overnight (disconnected from power).

I turned it on this morning with the immersion connector removed, so only the Immersun was starting up. Within 2 minutes the same is back. Looks like I'll have to send a message to Immersun.

As an update to this, Immersun's customer support was excellent. I ran some diagnostics at our end and the error persisted. Immersun organised for the unit to be collected by DPD – a week later it was returned, and it's working perfectly. So the error was related to the Immersun unit, not the immersion heater. 

Yesterday, my Immersun screen started flashing with the same error message.  'ERROR 8.  LOAD SHORT CCT,  CHECK: HEATER.

Unfortunately my unit is 16months old and I have discovered is now out of warranty.  

I contacted IMMERSUN, they say that is is unlikely to be the unit itself, and I should check the external equipment.  I have checked the supply from the MCB @240v, I have checked the resistance of the load circuit from the (disconnected) plug at the Immersun and with the thermostat contact made, it is 20 Ohm which is correct for a 3kW heating element.  Resistance to ground is 'OL' on my multimeter.  What else could be externally wrong that might cause this to happen.

Any ideas would be greatly received.

Do you still get the fault when the immersion heater is disconnected or the thermostat contact is open? If the fault is still present, then it could be a cable fault or the Immersun unit itself.

@julesmp8 that’s not great news. We did a bunch of “tests” connecting and disconnecting the unit from the immersion. Throughout the process, we were in touch with Immersun, and they requested we send the unit back because there was a hardware issue, but they never disclosed what the problem was; contrary info to what they told you.

I would, however, work through Derek’s processes. He’s very good at getting to the root of the issue.

Thanks for the info.

As mentioned I have checked all the wiring and I cannot find any issue which would suggest an external short cct.

I have also powered the unit up with the load connector disconnected inside the Immersun but the exact same fault appears.  Immersun have provided me with a procedure that performs a Factory Reset of the unit but that doesn't help either.

It seems to me that the fault has to be inside the unit but at a starting price of £169 for testing/ repairing this negates the whole reason for fitting the unit in the first place - to save money !  

@julesmp8 we did the factory reset too, which didn't help. I really like the Immersion units because they look really well built (far prefer them to the Solar iBoost) but there does sadly appear to be an issue with the units. 

Posted by: @editor

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@julesmp8 we did the factory reset too, which didn't help. I really like the Immersion units because they look really well built (far prefer them to the Solar iBoost) but there does sadly appear to be an issue with the units. 

Did you get your faulty unit repaired? What was the fault?

Hi 

So there appears to be only 2 options left available.  Prepay Immersun £179, send the unit to them and hope they can fix it (they quote a 85 - 90% success rate; charging either way).  

Buy something else to do the same thing.

Posted by: @derek-m

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Did you get your faulty unit repaired? What was the fault?

Yes, they repaired it. I enquired what the issue was but they said that they didn’t get a report from the repair team - it was clear they didn’t want to share what the cause was.