Stuart Turner Monsoon shower pump intermittent cut out fault - fixed

29 Jan 2011
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United Kingdom
Had an interesting fault on my Stuart Turner 2 bar Monsoon pump that I thought I'd share as it only seems possible to buy third party control boards for this type of pump - and even they cost upwards of £20.

The pump would intermittently cut out after it had been on a number of minutes. Turning the flow off on my shower mixer and back on again reliably restarted it, which initially suggested it was something to do with the flow switches. However, putting a magnet near the flow switch reeds had no effect when the cut out had occurred.

NOTE - the following diagnosis involved working on the pump/PCB with the mains supply connected so don't do this sort of thing unless you know what you're doing!

So I removed the PCB cover looking for any loose connections and found none. Then, I decided I'd fire up the pump with the cover off and check further - and I found by just lightly tapping the relay on the PCB, I could cause the same cut out to occur.

Next, I checked there were no loose screw terminals on the board, and all was OK, so it was out with the PCB to take a proper look.

I was expecting to see a dodgy/dry solder joint, but all looked fine. So I rigged the PCB up on the bench. The fault could be reproduced by tapping the relay every time.

At this point, I was starting to suspect the relay - but when I put my meter across the (48V) coil after I'd shorted the flow switch terminals out to operate it, I was only seeing around 12V DC which is way below the minimum operate voltage for the relay. So all it took was a light tap on the case of the relay and it would release and not re-operate on such a low voltage until the flow was turned off/on again - which I assume provides a little inrush spike which is JUST enough to operate the relay.

When the mains hits the control PCB, the first component it goes through is a safety/EMI suppression capacitor (the light grey item in the photo)- and putting my meter on the other side of it, I was only seeing a few volts AC - so it was clearly faulty.

The capacitor is a metallised polypropylene 220nF/0.22uF, 275V rated, and known as suppression class X2. The lead pitch on the capacitor was 22.5mm on my PCB. I found these capacitors to be widely available on ebay for under £3 inc postage, so ordered and fitted one (the replacement dark grey capacitor in the photo is a Kemet R46KN322000M1M). You can also get such capacitors from places like Rapid, RS, Farnell etc. too.

Job done.

Shower pump control board.jpg
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