wiring help....

Discussion in 'Plumbers' Talk' started by Chris J, Mar 15, 2022.

  1. Chris J

    Chris J Member

    I'm not sure how to wire a dual cylinder thermostat into this any help would be most appreciated . bc8ac5674a010c494cd00888963422f1.png
  2. andy48

    andy48 Screwfix Select

    1. to start with I think there are a number of issues with the wiring diagram:
    1a. Should there not be separate outputs from the programmer for each of heating and hot water?
    1b. Have the boiler connections been omitted. If so I assume there is a connection between orange in each motorised valve and boiler switched live.
    2. Do you mean by "dual cylinder thermostat" two cylinder thermostats, one in each of two separate cylinders?
  3. Chris J

    Chris J Member

    2/ see link will explain "dual cylinder thermostat" :https://www.cityplumbing.co.uk/RM-Cylinders-Dual-Thermostat-RPDS1/p/434565 I see I have dual and cylinder around the wrong way ....

    !a/ No programmer - it's a pellet boil so a self contained unit with no-way to operate the zone valves.
    1b/ see above.

    I hope tthis help to explain a little about the set-up.
    Last edited: Mar 15, 2022
  4. andy48

    andy48 Screwfix Select

    Thanks for the clarification.
    1. I don't know anything about pellet boilers, so I don't think I can help.
    2. The dual thermostat can be considered as two thermostats, connected in series so that:
    2a. If the water temperature is below that required, both thermostat contacts are closed.
    2b. As the water heats up, the "ordinary" thermostat part opens and breaks the circuit.
    2c. As the water cools down, the ordinary thermostat closes again and re-makes the circuit.
    2d. If a fault occurs and the water gets very hot (above the set temperature, but the ordinary thermostat has "failed") the over heat thermostat operates and breaks the circuit.
    2e. If the overheat thermostat operates it must be manually reset. It is not automatic.
    3. Not sure how all this works with a pellet boiler.
  5. Chris J

    Chris J Member

    I understand how it works just having a problem working out how to wire one into the above diagram.
  6. Chris J

    Chris J Member

    If it helps anyone else this is what I'm going with. bc8ac5674a010c494cd00888963422f1.png
  7. MGW

    MGW Screwfix Select

    Two type of duel tank thermostat, one is one thermostat does all, and second is a safety cut out. Other one thermostat turns on, the other turns off, this allows for a larger temperature differential so boiler does not fire up as often, and when it does has a longer burn, the latter would make sense with a solid fuel burner.

    With old gas or oil the boiler was cycled off/on, and pump would continue to run, since you wanted the boiler to cool, the C Plan or Y Plan was often used, as there was always some thermosyphon circulation even when motorised valves not powered.

    Modern gas boiler modulate, so often the pump and motorised valves are all part of the boiler, the installer has little to worry about, all built in.

    What worries me with any solid fuel boiler is over heating, we use them at work, coal fired, and the safety systems are really important, both to ensure boiler does not run short of water, and to allow excess pressure to escape.

    Whole idea of a valve to stop flow seems wrong.

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