Sorry, removed previous reply as I had missed the word 'unvented'. I think it is trickier with an unvented to add in a retro-fit coil.

A couple of the moderators tried to steal all the user data for their own ventures. Was closed down in haste, sadly, instead of transferred/preserved to a new home.

Hi Steve, Your second image is the fill/flush point for the system where you can re-fill and re-pressurise it. That's the first task and then perform a leak check. Pressure wants to be around 1 - 1.5bar. If no leaks it should hold but will over pressurise and blow off if there is no heat being circulated / dumped into the pool. The controller will most likely need replacing but it having the pump stuck on will be no bad thing for now as you'll be able to tell if the heat is transferring once it's re-pressurised.

Hi Nigel, I have a contact near Fishguard who should be able to help. If you could drop an email to sales@stovesandsolar.com I will send you his details. Thank you

Doesn't it just. A shame we were sabotaged before we got started. Work is being done to bring back the old forum

Hi Mike, if it is the original model (TDC3?) then it has done quite well to last this long. The current version is the MTDCV5, available in the Solar Controllers section

@mahemingway7 Hi Mike, to be honest, I can't recall if Frost protection activating is something that would show up in the message log. I'll do some digging

Hello, where are you based?

Hi Mike, if the replaced S1 was at 4degrees and the system continued to pump, that leads me to think the frost protection was kicking in. Were it not working and treating it as usual activity, it would have stopped pumping.

@tim It depends if a bleed point was fitted. Some installers put one in on the inside of the roof, higher up than the panel itself

Hello Tim, there isn't an instruction as all systems potentially could be different but there is a standard schematic in the Documents and Downloads section which may help.

I see. One way to check is to put S1 in a cup of ice and see what happens. If S1 is too difficult to access (being in the panel and on the roof) wire one of the other sensors temporarily into S1 and use that. Then you'll know for sure if it's working or not.

Hi Mike, is there antifreeze in the system? What makes you think the frost protection is not activating? Can you hear the pump coming on at night? It can only be a few quick pulses on and off to keep that system temperature above freezing. Thanks

Ah right. I don't think I've seen any in the warehouse for years now because it's been so long since they were supplied. I'll keep an eye out though and if I find any I will drop you a message

oh nice! thanks for sharing!

The tubes sound like they are broken. Probably just hairline crack which could've been caused by anything. The reflectors are no longer supplied. They're more hassle than they're worth and I would recommend binning them.

Hi, you can check none of the glass vacuums have been compromised by looking at the bottom. If they're silver, they're intact but if they've gone cloudy white then the tube is cracked somewhere and the vacuum has gone.

When you say electric, are we talking immersion heaters? Top and bottom? Will you have/consider an immersun style diverter for solar PV?

Yes, a lot. Typically I would draw my schematic based on what I want. For example, your thermal store, then each heat source you want going into it and from that I can work out what needs to be controlled in term of pumps and valves and apply a suitable controller to it.

@robin.deas Ok, do you have a schematic of the system?