Immersun issue, help required as they have ceased trading

Hi i have had an Imersun 2 years and it works fine, it feed into a 3Kw load via a switched spur with neon,the other day i noticed the neon still on although i had a tank of hot water, so i measured the voltage on the live side of the thermostat and had 240 volts,( hence the neon still on).
I then ajusted the stat to give a demand to the Imersun and it responded correctly, i tried to contact 4 eco and they sent me an e mail to say they had ceased trading and could not help, this was yesterday 30 June.
i have isolated the emersion heater and the 240volts is coming from the Imersun, it does not affect the operation of the Imersun but i would like to know what has caused this change.

[I’ve corrected the spelling in the title so that it’ll show up in searches.]

I don’t understand what the actual fault is from your description. Is it a faulty indication only, and in fact the Immersun is operating correctly as far as you can determine, or is the Immersun output permanently on and the immersion heater is now controlled only by its thermostat?

If it’s not working, you can’t repair it and you need a replacement, you could do worse than look at

Do you have any detailed technical information (circuit diagram, parts list, etc) for your failed unit? Without that, it’s going to be hard to offer anything other than the most general guidance.

Thanks for your reply Robert, i do not have a fault it is just a change in operation,when the water is hot and there is no demand i have 240v feeding the open side of the thermostat, i have never used the boost button,i have no technical info or circuit diagrams, its just a glitch, maybe a relay has failed.

It’s highly likely that the Immersun relies on the immersion thermostat to control the water temperature. MartinR’s original diverter design (not the one published here Learn | OpenEnergyMonitor) used a measurement of water temperature to control the energy diverter, leaving the thermostat as a safety backup. However, this required extra sensors and wiring and I can easily understand why this approach is not generally used.

I’d be surprised to find a relay in there. Most likely, the switching device will be a solid-state component and (depending on which model you have) could be either a triac or a power transistor or a pair of power transistors, probably field-effect devices.

Is it possible that your Immersun is simply operating in a mode that you haven’t (knowingly?) experienced before?

The Immersun detects whether the hot water tank is hot by checking whether the immersion heater is open-circuit (meaning the water is hot). In order to detect the state of the immersion heater, a live signal has to be present at the immersion heater (and the live side of the neon). Could it be that the other side of the neon is somehow earthing on something allowing sufficient current to flow to light the neon, but not sufficient to heat the immersion heater, or to trick the Immersun that amps need to be applied? I’ve certainly had neons illuminate in the past even when they don’t appear to be connected to anything to close the circuit…

Main question is whether the Immersun reckons the water is hot. If so, it doesn’t sound like this is faulty. If I get chance, I will take a reading of my immersun output when the immersion is hot (could be a few days, given the bad weather we have this summer). My suspicion is that I will see 240V, even without any (significant) current flow as part of the monitoring system to detect open/close circuit for hot/cold water.

It’s a real shame Immersun have ceased trading. I just wish I knew the API to be able to interrogate my Immersun locally… {sigh}

Thanks Ian,
I have a tank of hot water, the Imersun display reads hot water,the thermostat is new, i still read 240v on the live side of the stat, i took the cover off the Imersun and measured the output cable conections and i had 240v on the dvm.
The Imersun is working ok, so maybe its nothing to worry about.

If anybody can provide accurate details of what’s inside the Immersun (circuit diagrams & parts lists especially), it might be possible to establish whether there is a fault or not. (And we could have a stab at supporting customers who’ve been let down by Immersun’s demise.)

It depends on how they check the state of the 'stat. If they bleed a low current (mA) from the supply and check the voltage, it’s indeed likely that it will light a neon (connected line-neutral across the supply side of the isolating switch) when the 'stat is open, but when the 'stat closes, there’s insufficient current to do any heating. Alternatively, they could fire the power switch and look for current in the immersion feed (if it’s monitored), or a matching change of current in the grid infeed.

I don’t quite see what you mean by [quote=“pagewrite, post:5, topic:886”]
Could it be that the other side of the neon is somehow earthing on something allowing sufficient current to flow to light the neon, but not sufficient to heat the immersion heater, or to trick the Immersun that amps need to be applied?

If it was a neutral-earth fault, then if the circuit is protected by an RCD, it’s likely that the RCD would trip in that case.

I’d guess that there was enough capacitance in the cable to complete a circuit including the neon to provide the few mA necessary to light it.

The other place for a neon is ACROSS the 'stat contacts, thus indicating “Hot Water”. This is highly unlikely, and doesn’t fit with the description of a switched spur with neon.

An announcement has now appeared on [the Immersun website] (

It would appear that the Immersun name is now owned by another company, Sisem Ltd. Some company details here.

The website is live at the original Immersun URL.

The Immersun main site is up and running but the server storing the usage data ( shut down on 31st August.

Unfortunately I was using this data to determine whether the installation of a battery system would be beneficial. My unit is performing normally just no display of the data. I am not sure what my alternatives are at the moment. Any advice?

I rather suspect that your historical data is lost forever. That, unfortunately, is the price you pay for relying on others. Immersun have historically been fairly hostile in their advertising, so I would rank the likelihood of being able to access the data from the Immersun unit as being quite low, unless (a) it’s not encrypted and (b) you or someone else has the time and ability to decode it, or (c) the new management has a change of heart and publishes an API.

You could buy an emonPi kit with a couple of CTs (assuming you have PV) which would give you a measure of wherever you installed the CTs - one presumably to monitor the nett grid power, the other for whatever. Presumably again, your PV meter gives you the total generated energy, but your tariff meter only shows imported energy. At least with an emonPi, everything is under your roof under your control, and you can export to as well if you wish.

Does anyone know any member of the Immersun team, who may be willing to update the system and charge a yearly fee so we can receive the data and see our equipment in real time again on our smart phones.

I had my new immersun V2 unit fitted end of April 2016. The Immersun team members were extremely helpful. Maybe you could find their names via linked in etc and they may have the ability to put you in touch with the right individuals.
Lee Sutton: Technical Services Director
Lee Smith: Head of sales

On a personal note. I am extreemly keen and would be willing to pay to have the graphical data up and running again via the app or

SISEM are just getting up and running, the online monitoring was working for a couple weeks and has suffered an outtage for the last week. As of today though its back up again.

I’ve created a facebook group to try to bring owners together so we can work to resolution for any problems we might have.