Unvented Cylinder thermostats

[Jonm]

My installation is about 3 years old, professionally installed in a new build house. I have a vitodens boiler, Evohome controller, hr92 valves in 12 zones, 2no bdr91 wireless relay boxes, cs92 wireless cylinder sensor. I also have a Codice cylinder stat which acts as a secondary cut out.

The cs92 has a probe sensor inserted in a tube in the indirect, unvented tank about 40% up from the bottom.

I had hot water running in the tun dish, flow like a tap half bore. Now when I switch on the hot water the water gets to about 30 deg C as registered on the controller, warm water flows in the tun dish and the water from the taps is warm. I am arranging for a plumber to check the expansion vessel and change the temperature pressure relief valve.

I wish the plumber to check/ change the temperature sensors to be sure that the problem was not caused by the tank overheating, the water was very hot when this problem occurred.

My questions relate to the temperature sensors. The wiring is in series as follows. BDR91- codice cylinder stat - motorised valve - vitodens 7296968 (which converts mains to low voltage and connects to boiler.

The codice cylinder stat acts as a safety cut out, it has two sensors, one for temperature (variable set at 65 deg C) and one for overheating. The sensor for the cs92 is in the same tube as the codice sensors.

I am intending to change the sensor for the cs92 and am inquiring if there is a way of providing an overheating cut out to replace the codice cylinder stat. Also is there any way that I can test that the sensors are all working correctly.

I attach a photo of the cylinder stat with third sensor from the cs92.

[Jonm]

I thought it may help if I post the wiring diagramS I have drawn of the system as installed


Schematic

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Detailed

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