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Relay chatter on heating call

Postby LinHesEN » Fri Oct 01, 2021 11:29 am

So my heating decides to go south just as the weather goes downhill.

I'm not a gas engineer / sparky so apologies for stating the obvious or simplifying things!

Fairly sure I have an s-plan system (2 x 2 port values giveaway), Ideal Classic FF240 (old but reliable), and a bog standard Drayton RTS2 thermostat (2-wire install, 24V). (Frost thermostat above boiler but I can't imagine that is the culprit but willing the be corrected!)

Hot water is fine but any call by the thermostat for heat results in relay chatter (photo of junction box + relay attached)

I've isolated the thermostat and replaced the relay with no joy; the relay seems to be fed around 10-11Vdc - above the pick up 9.6 but I'm assuming my cheap multimeter is reading correctly. Relay coil operated using a Creston PWI-1210 (top left of picture). I can't find any obvious loose wires in the junction box.

The switch to the left supplies the transformer and to be honest I haven't to a clue what function it has in the junction box. Either way if this switch is OFF and I manually close the relay I can operate the heating via the programme timer - this is my current work around but isn't ideal as the room thermostat is taken out of the loop so full blast heating it is.

Other than replacing the supply that switches the relay am I missing anything obvious here in what could be causing the relay to chatter? At one point it would chatter but for then was fine, but now it is constant, which sort of points to a partial then full failure somewhere.

Anyway, any pointers much appreciated.

Junction box + relay stuff
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