Combi Boiler woes - first heating & no DHW, now DHW and no heating....

[RichardS]

Think our ageing Ocean FF combi (sorry, can't see any identifying model mark other than this and the serial no. on or in the casework) is telling us that it needs some care and attention, or that we ought to speed up our replacement plans....

For a couple of days I had noticed that the hot tap needed to be turned further and further on before the boiler would fire into action. Yesterday morning it decided that no amount of flow was going to wake it up.

The boiler has a selector switch for DHW only or Heating and DHW. I turned this to DHW only and then back to the DHW + Heating setting, and all was fine again - boiler sparks into action immediately now when the hot tap is opened (it's mounted on the kitchen wall, about 1m pipe run from the hot tap).

However, the heating refuses to fire up at all now. All thermostats checked and set to max for the moment - they are definitely both past the "heating on" clicks.

The pump is slightly warm to the touch, and I have tried the normal percussive attack on it and twisting the spindle doesnt seem to make any difference.

Any hints on where to start with diagnosis/fix?

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[John]

IMHO this is one of lifes nasty fiddly repair jobs. Fortunately it is likely to be a diaphragm assembly which has failed and a service kit is fairly readily available. Fitting it is another matter and bits fall out everywhere when you start to open up the diverter block Good luck!

[Hugh]

possibly a dhw heat sensor? sorry don't know your make of boiler at all, but Worcesters that I'm used to. If the heat sensor gets 'furred up' it's a simply job to change, and very cheap - it would cause the symptoms you mention as it's not giving a signal to the boiler to fire-up when required. I believe they are also called flow sensors, but whatever, it's a good starting point as it can save a lot of expense, etc. if it is the fault.

Hugh

[RichardS]

Thanks - sorry for not responding sooner but my ISP's news server hasn't replicated any new articles for the past two days (I did see them from a free - ie no post permissions - server that I use but couldn't respond).

What I'm seeing after further investigation is no voltage at the pump when the heating should be on. I would have thought that the first thing that gets fired up when switching the heating on is the pump, and the boiler then kicks into action from a flow sensor on the heating circuit - ie fail-safe in case of problems with the pump. Perhaps this is not the case though.

Why would you suspect the diaphragm assembly? (just curious as to the diagnosis)

many thanks

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[RichardS]

the pump isn't firing up either - I would have expected such a failure to result in the pump runnign without the boiler firing up, perhaps?

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[John]

Based on the build up period where you had to run more and more "hot" flow to get the boiler to start. I'm guessing the diverter assembly has now stuck in a mid to hot water only position. Only a guess from afar at this juncture I'm afraid. Of course it might be something else entirely but then again you could have two simultaneous faults :-( Personally I'm not at all impressed by the model you have. Lets hope the latest output currently being promoted from this manufacturer is built of sterner stuff

[RichardS]

OK, thanks, that sounds reasonable.

No, I'm not particularly impressed with this model, but it is now quite old - I am guessing 10 to 12 years, could be more.

Replacement is on the cards, but I have now got a service call booked (the thing burst into action again last night) with a heating engineer, so hopefully it will last for a couple of months until I can get the cash together for something rather better.

Vaillant and Wocester-Bosch condersers look most likely at the moment.....

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[Ed Sirett]

Is this model one where the diverter valve is operated directly form the DHW flow, so that if the diverter valve sticks then DHW mode is not attained?

[John]

Take a look at the Glow Worm 30 models in either condensing version or non condensing version