Central heating query

[MalcParticipant @malc]

Hi all,

A little off subject here, but knowing the range of experience between you all I thought it was worth a punt:

I have just fitted a Drayton RTS9 room stat, 4 wire connection, (L,N COM & CALL) with an indicator light. When fitted the indicator light was on when the room was calling for heat whether the system was programmed on or off. I preferred to have the indicator light lit only when the heating was programmed ON and calling for heat. I removed the permanent live and replaced it with a link from the COM as this is only live when the programmer switches on the heating. This is working OK but I have noticed that the indicator light glows dimly when the heating is programmed off and not calling for heat, does anyone know, is this to be expected?

[MalcParticipant @malc]

[davebParticipant @daveb17630]

It sounds like a neon indicator, they do this if there is some leakage current.

[Les Jones 1Participant @lesjones1]

I agree with daveb. I suspect that the cable between the boiler and the thermostat is a 4 core cable. there will be capacitance coupling between the permanent live and the live that comes from the time switch in the boiler. This will provide a small current when the time switch is of which is enough to light the indicator lamp dimly. (This is a problem that I have seen with LED lighting. ) If you measure the voltage between the neutral and live terminals with a digital multimeter you will probably get some reading when the time switch output is off. If you add a small extra load between the live and neutral terminals it will probably solve the problem. You can confirm this theory by connecting 1 15 watt filiment bulb between the live and neutral terminal. When I have has a similar problem a have used a capacitor to provide the extra load as this does not produce any heat as would be the case if a resitor was used. I normally use a contact Suppressor such as this (Which is a capacitor in series with a low value resistor.) as it is packaged with flexible leads which make it easy to install.

Les.

[Brian Sweeting 2Participant @briansweeting2]

If you wire it so that your timeswitch supplies power to the thermostat then there won't be any power to it during the OFF periods.

[Les Jones 1Participant @lesjones1]

I think that is the way that Malc has connected it.

Les.

Edited By Les Jones 1 on 24/12/2017 17:09:18

Edited By Les Jones 1 on 24/12/2017 17:09:37

[MalcParticipant @malc]

Hi All,

Many thanks for the interest. Yes, I have connected it to be supplied from the controller, which is why I was surprised when the indicator came on with the controller off. Thanks Les, I will follow your suggestions after the turkey etc., have checked my shed stocks but, as usual, everything but the thing you want! Thanks again all, and a happy Xmas and new year to you.

Malc.

[Les Jones 1Participant @lesjones1]

The best place to find suitable capacitors is in the mains input filter of a switch mode power supply. (PC power supplies are switch mode so you might have some old ones.)

Les.

[MalcParticipant @malc]

Hi Les,

Thanks again, you are a real font of knowledge. Now go and enjoy your Christmas and don’t worry about old farts with dodgy heating!

All the best,

Malc.

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