Drayton SCR and RF 2 fault finding

March 6, 2013 at 5:57 pm (house) (, , , , , )

We’ve been having some issues with our central heating.  A couple of weeks ago it stopped coming on completely.

A bit of debugging seemed to be showing that the thermostat had stopped asking the heating to come on.  Sure enough, when I bypassed the thermostat by adding a loop wire back into our boiler (as per the manufacturers default ‘as delivered’ state) I was able to control the heating manually, so I knew the boiler was fine.  So what to do about the thermostat?

Well I could go out and buy a new radio thermostat for £100-150, but thought I must be able to do better.  We have a Drayton SCR receiver and a RF 2 controller unit.  It all looked like it was working.  The green light came on when the override was pressed, but the heating wasn’t triggered.  I could also see the red light flashing when the controller was asking for the heating to trigger – but still no signal to the boiler.

Eventually, after trying the ‘learning’ mode and commissioning sequence as per the manual, manufacturers troubleshooting guide, and general Internet wisdom, I eventually found a site that said that the SCR units can develop a fault over time where the large capacitor on the circuit board degrades and can’t maintain the voltage required to actually switch the boiler.  That sounded promising so I found a replacement capacitor on eBay for £4, waited and when it arrived got my soldering iron out.

That did the trick!  All working perfectly then for around two weeks.  Then I had a different problem.  This time the red alarm led was always on.  Again I went through the commissioning sequence but no luck.  I reset the controller as per Internet comments – removing battery draws, etc, still no good.  I tried new batteries too, but still no good.

Then I found a note that the last hand battery drawer was the display and the right hand drawer was the transmission circuits.  So as the display was all fine, I wondered if there could be a fault with the radio side.  The contacts looked a bit dirty, so I got the polish and a cotton bug out and gave them a clean.  That did it!  Even though official fault finding seemed to say the unit would be faulty, it was just dirty contacts in the battery drawer.

So, with a bit of logic, Internet support and willingness to think the problem through, our heating is all fine again now and so far (fingers crossed) I’ve not had to spent £100 plus to replace a thermostat that has otherwise worked fine for around 10 years.



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