My boiler is controlled by a programmer unit to turn on and off at certain times. There is a receiver unit between the programmer and the boiler, and I believe this receiver unit is at fault.

The problem I see is that sometimes the boiler comes on at the correct time, but shortly after (sometimes seconds or minutes), switches back off again.

I have found that I can make the JQX-115F relay component switch on and off simply by moving the receiver unit from side to side. My understanding is that the relay should be switched by application of 24V DC.

So my question is, if the relay is switching as I move it, does that imply the relay is at fault, or could it be an input to the relay which is at fault?

(I ask because this receiver unit (Nobo RSX 512) has been discontinued, so I'm not sure I can get this repaired without changing the entire setup, or understanding and replacing the faulty component.)

JQX-115F relay on Nobo RSX 512 receiver unit circuit board

  • 1
    Most likely a loose connection somewhere
    – NMF
    Sep 15, 2019 at 12:02
  • Thanks @NMF, I once sprayed electrolube on the four wire connections on the right of the picture, and it seemed to have helped, but only for a while. I have removed all of the wires and retightened them, but it's not making any difference. Anywhere else there could be a loose connection?
    – Tim Iles
    Sep 15, 2019 at 12:13
  • what is shown in the picture? ... the wires appear heavy enough to be AC power connections ..... hold the module that is in the picture very firmly so that it does not move, then wiggle each component to see if the problem occurs ... be very careful because that module may be at line voltage
    – jsotola
    Sep 15, 2019 at 20:42
  • if movement and time are both factors, then you almost assuredly have a loose connection that heat disconnects due to uneven expansion/contraction.
    – dandavis
    Sep 16, 2019 at 5:07

2 Answers 2


From your comment, it seems most likely that one or more of the solder joints that connects the green terminal block on the right to the PCB is dry, cracked or is somehow otherwise failing. Strain on the PCB connections from the wires pulling on the terminal block is the likely cause.

  • I think you must be right. It's currently stuck permanently on since I electrolubed the terminal block. This is better than not working at all, so I'll leave it for now, but next time it starts being flakey again I'll investigate further.
    – Tim Iles
    Sep 22, 2019 at 12:13

not sure how handy you are, but you could take the board out inspect it, check all the diodes, resisters, and if any test bad or cracked, etc. using a soldering iron and repair board. the color bands on the resister tell you what ohm's rating is.

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