Keston C36 No hot water in morning

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31 Dec 2021
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United Kingdom
Hi everyone,

I can see a few people had this issue, but its not entirely clear if or how it was resolved, so I'd really appreciate some help here. The symptoms are as follows:

  • Open hot tap
  • DHW demand light stays dark
  • Display temperature remains constant/room temperature
  • Water is cold
  • Central heating comes on if called
  • After some time of turning tap on and off, finally, panel temperature reads the cold pipe/8 degrees of whatever and hot water/DHW light comes on.
  • Works for rest of day.

Work previously done:
  • Diverter valve is relatively new
  • Thermistor is also relatively new
  • I recently fixed a couple of water leaks (maybe it has become humid in there and damaged electronics?)

There's a resistor on the central heating flow sensor's wiring loom that looks like its corroded, but it feels like a stretch that this could cause it....

Any ideas? Very difficult to get someone out to look at the boiler these days

many thanks
David
 
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Most engineers will start to develop symptoms not unlike PTSD at the mere mention of a Keston.

Does that model have a flow switch, and is it working?
 
Thanks KidGreen, yes like most people who have them, mine came with my flat. I wonder if anyone ever actually buys them or of they install themselves in unoccupied houses. Oddly enough theyre not even cheap!

Ive looked through the manual and can only find a flow switch that pertains to the CWS. I've heard it said elsewhere on this forum that this model works off a thermistor on the hot water pipe (so seems to agree with the manual)... but then the contradiction is that if I look at display 8 of the installer readouts, I can see the hot water demand value that changes too quickly for a thermistor on the outside of a pipe when I turn a tap on/off/up/down... so I guess it must...? I cant physically see it either
 
Ah, I think this same flow sensor is in fact both for CWS and DHW! I guess this or its associated wiring might be the likeliest source of the issue
 
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Hi Ian, the one on the hot water pipe. Looking more closely it looks like there is a capacitor in the block connector for the flow valve and it looks to have been corroded. One of the legs is broken, but touching. I cant see what capacitance of this is, but it seems to work having taped the leg on, though the issue is sporadic (so it might still happen again)
 
The CWS flow sensor is the demand switch, when a tap is opened that sensor tells the boiler HW is needed and fires the boiler up. If that is corroded then that would be first thing to change IMO.
 
Thanks Rob. (PS its not the sensor itself, it seems to be a small capacitor on the flow sensor's wiring loom, but this must be part of the flow reading circuit)
 
Not sure about that make TBH, never had the pleasure ;) and not sure whether the loom is all in one, if so I guess it might not be cheap to replace. Also not sure if it is a room sealed case or not?
 
The loom does look like an 'all in one' and would be pain to get at. Probably best shout is the tape for now...and if that fails, maybe I can replace the capacitor itself/its just sitting in the block and relatively accessible. (If I can figure out what the cap is)
 
Just to update; changing the capacitor out fixed it. The Keston C36's flow sensor has a ceramic 100uF (104) capacitor in a block connector between the sensor and the control module. If this is bad, a good flow sensor will return wild readings, and/or none at all. Thanks all for the replies!
 

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