No Hot Water unless...UPDATED

[conny]

I have a Jaguar C/H combi boiler and recently the hot water side has been playing up.

If the heating is on the water will get hot if the heating is off the water won't heat up when a tap is turned on. I have removed the covers and found that one of the thermocouples has what appears to be an electrical arc burn on the ceramic casing, could this be the problem and if so would replacing it solve the problem?
Thanks in advance, I have posted a picture to help.
A galvanised cover plate goes over this and actually touches the ceramic just where the burn is.

 

[DP]

Conny the item you call a thermocouple is in fact a spark electrode. If boiler functions for heating, I would say the spark electrode is in perfect condition. If it were faulty, you would get no heating or hot water.

Fault would seem to be in 'hot water detection' area. Running of hot tap is 'seen' by the boiler. Boiler then self starts to heat water.

Running boiler in CH mode means boiler is already running when hot tap is run, so you get hot water.

Suggest you put the cover back on the boiler- not safe to remove it and run the boiler

 

[conny]

DP,
thanks for the reply.
Can assure you cover is on and secured properly!
To the right of that electrode there are 2 similar probes, I suppose these must be the thermocouples but both appear ok and are in the flame when the heating is on.
It was only removed for 'inspection' purposes. Looks like I will have to get an engineer out unless you have any suggestions of where I should look.
I can assure you that I will NOT tamper with anything unless I am sure what I am doing and I certainly won't touch the gas side of things.
Once again, thanks.

 

[ollski]

I'd be starting with the hot water diaphragm in the diverter valve

 

[tdesnos]

sounds like the flow switch mate. sometimes they can be freed up like on the baxi 105 there's a little spindle that you can move backwards and forwards until it becomes loose again, sometimes they're internal in the pipe.

 

[conny]

Thanks for the replies lads.
The diaphram was replaced about 2 years ago, as for the flow switch, I wouldn't know where to look for that so looks like an engineer is called for.
Impossible question probably but what kind of price would I be looking at for a repair. Worst case scenario.

Once again, thanks for the replies.

 

[dextrous]

Impossible question probably but what kind of price would I be looking at for a repair. Worst case scenario.

£500000000000000.01 +vat

 

[conny]

£500000000000000.01 +vat

Is that all?

Do you know his name and number?
Is he gassafe registered?
Can't be for that price.

 

[ollski]

The diaphragm is the flow switch in tandem with a microswitch at the other end of the diverter valve. The diaphram will have a hole in so as not to move far enough with a demand to make the switch but far enough to open the hot water port in the valve so it flows through hot from the ch demand. The other option is that the spindle has leaked into the microswitch causing it to fail. I would imagine around 50 quid for option 1 and 80 for option 2 without checking exact prices. (the diaphragm won't be available as a jaguar spare but maybe as a glow worm / biasi one)

 

[conny]

Update on this problem.

Found my owners manual earlier and found a trouble-shooting section.
Led me to check the resistance of the hot water thermistor which was easily found and to my surprise one of the leads was hanging off. Took it off completely and checked the resistance, because it was on a hot pipe it was not accurate to the book figures,
10kΩ @25°C
12.7kΩ 20°C
16kΩ 15°C

But I managed to get differing readings as it cooled down.
I secured both leads back on and re-clipped back onto the pipe, closed up all the covers ensuring all seals were properly mated and switched the water on.

Hey Presto!
Boiler ignites and hot water flows!
Have tried it a number of times over the past hour and it works!

Thanks for the previous replies lads, I thought it fair to let you know the final outcome.


Dex, thanks for the tip but I've just saved myself £500000000000000.01 +vat


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