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Solar Thermal System Design Issue: Resol Delta Sol BS Plus controller

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Active Member Member
29 kWhs
Joined: 1 week ago
Posts: 2
Topic starter  

I have a solar thermal system with a Resol Delta Sol BS Plus controller. I have recently had some works done to the system and since then it does not appear to be functioning properly and I wondered if anyone had any ideas about what could be wrong.

The issue is that when the system’s pumps turn off, either because a store has reached its max temperature or because the system is checking its temperature during an Oscillating Break Time, the system (through the collector sensor) no longer detects an increase in temperature at the top of the collectors.

What happens is that the pumps turn off and the collector sensor actually registers a decrease in temperature at the top of the panels. This goes on for as long as the pumps are off and the temperature just falls steadily.

If the pumps are turned back on manually, the flow of the system start circulating again, the temperature reading at the collector sensor then rockets up by 10 – 20 degrees or more and then levels out once the pumps have taken back control, released the heat through the heat exchangers etc.

It’s an issue because it means that (a) the store prioritisation is no longer working properly and (b) the system doesn’t detect when it’s about to overheat and so doesn’t restart the pumps in an emergency fail-safe function (e.g. under the OREC or OCX functions).

It didn’t used to be a problem. On a sunny day, what used to happen is that when the pumps turned off, the collector sensor would detect a steadily rising temperature and then the system behaved as expected, heating the stores in the right priority… with the other system controller functions etc.

Has anyone ever heard of or encountered this issue?

This topic was modified 1 week ago by Mars

Illustrious Member Moderator
13948 kWhs
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Joined: 3 years ago
Posts: 4196

What work was carried out on your system? Did the people carrying out the work not test the systems operation after the work was completed?

If possible I would suggest that you call them back to rectify the problems it would appear that they created.


This post was modified 1 week ago by Mars

Active Member Member
29 kWhs
Joined: 1 week ago
Posts: 2
Topic starter  

The work involved upgrading a lot of the pipework and the circuit pumps and installing a new third circuit.  The people who installed it are struggling to identify what the problem is.  They're coming back again next week but I'm trying to get a head start on the issue to understand from all the experts out there whether anyone has had this sort of issue before, or if anyone has any ideas as to what it could be, so I can make sure things are steered in the right direction.



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