Keston C36 No hot water in morning

[MDavidM]

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

 

[kidgreen61]

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?

 

[MDavidM]

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

 

[MDavidM]

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

 

[ianmcd]

Which thermistor did you change ?

 

[MDavidM]

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)

 

[Madrab]

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.

 

[MDavidM]

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)

 

[Madrab]

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?

 

[MDavidM]

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)

 

[MDavidM]

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!