Underfloor heating control system teardown (with schematic)

This is a set of fairly common Polypipe controllers that interface an underfloor heating system to an existing heating boiler. There are two modules - the main one and then optional slave modules that allow extra thermostats and manifold valves to be used with multiple zones.
It's a very simple and neat arrangement that literally just plugs end to end to build up the desired number of channels. It also has a DIN rail mounting facility for use in panels.

There's a story behind this. Some elderly friends asked if I could check out their heating system as they had an issue with it. The issue turned out to be that while renovating a cupboard they had mistaken the manifold and wiring for their new underfloor heating system as being part of the old and obsolete heating system.
They laid into it with wire cutters (while it was live) stuffing the chopped wires back into the plasterboard they were sticking out from and also pushing them down under the floorboards (while still live).
The original controller in that section - the master unit shown here, was then thrown in the bin.

It was one of those "wish I hadn't got involved" moments. Their original heating engineer who installed the system was no longer living on the island and other heating maintenance companies had declined to get involved.

I had to identify the control system from the modules in use on other parts of the system, download the manual, work out what component was missing and replace the chopped cables.
Initially I just reconnected the boiler control line so that the rest of the system could control the boiler, then when the replacement module arrived I used the handy existing mounting holes to fit it, and reinstated their system to its original form.

During the research on the system I bought a few cheap modules from eBay. It seems to be a common thing that people enthusiastically buy complete kits for installing underfloor heating and then subsequently realise it's not just a case of banging down pipes and hooking up a few wires. They then sell the unwanted components on eBay at a greatly reduced price.

One of the notable design features is the use of a standard 230V AC relay with a capacitor across its coil to allow it to be actuated by multiple circuits via diodes. That effectively saved the use of a relay per channel. The rest is fundamentally a wire marshalling box with diagnostic indicators.
The terminals are reassuringly good quality rising clamp modules with a generous cable capacity.

I also got some of the thermal manifold actuators, so I'll take one apart in a video at some point.

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