Help diagnose a fault on an oil combi boiler.

[ProDave]

Todays estate agent fault to look at. An oil fired combi boiler where the hot water is not working.

It's a Camaray 5 Combi 90B external. A make I have not heard of, but looks remarkably similar inside to a Grant, which is a common make of outdoor combi oil boilers.

Of course the fault is intermittent and when I was there it worked perfectly.

When it goes wrong, they say they get a short burst of hot water, then it goes cold, but if they turn the heating off, then the hot water works.

The way this boiler works, is there is a flap type water flow sensor that activates when you start drawing off hot water. That turns off a motorised valve, which shuts off the heating flow and diverts it to the heat exchanger plate for the hot water.

Now my thinking is the flow switch is the likely fault. If it were the motorised valve then I would expect the fault to be "no heating" as the motorised valve has to energise to divert the flow to the radiators.

Anyone agree or disagree with this diagnosis.

As I say it wouldn't go wrong when I was there, so changing the flow sensor seems a simple first step, and at least will rule that out if it doesn't fix the fault.

 

[Smilers]

Sounds like at boiler valve is letting by! How old is it Dave perhaps some scale?

 

[ProDave]

Can't say the age for certain, but it all looked clean and fresh inside and out, so probably no more than 10 years old.

Scale is not usually a problem up here, most of our water comes from mountain lochs and is nice and pure.

 

[Smilers]

Intermittent faults are simply pants! Change this bit replace that bit and it's still a problem arggggggghhhhhh!!!!

 

[steptoe]

I'd go with you on the sensor Dave,

is it a cheap(ish) and simple enough job?

worth a try then.

 

[ProDave]

Yep I'll try a sensor first and see how that goes.

Now where do I buy one?

The boiler is a Boulter Camray 5 Cobmi 90B External. Googling that gives me the installation manual, it's made by part of the Worcester group.

The sensor is a Sika VKX 15M and googling that gives me a PDF that describes it and confirms it is the part I want, but I can't find anybody selling it.

I'll phone the merchants tomorrow.

The manual fault diagnosis for no hot water lists flow sensor, relay, and motorised valve in that order. So I'll try replacing them in that order until it's fixed.