The problem and solution is really quite simple, and incredibly cheap if you can wield a soldering iron. The issue is not the relay itself, but the rather crude power supply. There is a 22uF electrolytic capacitor which smooths out the 50Hz from the mains, which due to the high temperature it is constantly exposed to, has dried out, and consequently is no longer doing a very good job. The buzzing noise is the relay being switched on and off 50 times a second - which isn't very good for the pump. Maplin supply suitable electrolytics that are rated for high temperatures - so should last a few years longer. I suspect that replacement boards will develop the same symptoms over time. I've replaced all the electrolytics in both boards for around 50p[/img]
I went to the Pump Drive PCB first and found discolouration from heat scorching on the PCB. I started to undertake some resistance checks and damn near burnt myself on Delay Timer PCB. It turns out that the heat scorching originated from R1 on the Delay Timer PCB. I haven't had time to desolder for proper testing but resorted to a quick voltage check in situ. The right hand leg was at 125v and the left hand was at zero. This can't be right 125v dropped over one resistor, can it?. Does anyone know the R1s component data and value so as I can replace it rather than the whole board?
Thanks to all who contributed answers here. I had the same relay chatter (buzzing)with my Boilermate II. Replaced the smoothing cap (22mF 63V) on first the pump delay PCB, that changed the buzzing to more frequent and regular. Then changed the 22mF 63V electrolytic on the pump drive PCB, finally "Peace at Last" (as PAL TV was once known...)
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