DIY Doctor UK DIY Forums

Hi
I have an Ariston Genus27 MFFI combi boiler installed in 1999. It has given me very few problems. However, this week the hot water will only work when the central heating is on. More specifically, when the main burner is ignited.
If the boiler is switched to hot water only, or if the boiler is switched to central heating and hot water but the central heating is either timed off or switched off by the thermostat then I do not get hot water.
Any ideas please.

Check the diverter, may be a stretched or split diaphragm, therefore the pin will not connect with the microswitch to bring the boiler on.

htg

Thanks for your prompt reply htg.
I have now found I can activate the microswitch manually at the right of the divertor valve to ignite the burner, which I reckon must support your theory.
I have some plumbing experience but its very limited with boilers. However if my wife tells me once more there's no hot water I think I'll go nuts.
Can you advise on the most difficult part of the job so I can gauge my competence rather than come across it at the halfway stage. Access to the pipes below the divertor valve looks particularly tricky.
Thanks

Hi Barry,

Turn power off to boiler and protect the leccy bits is often forgotten.
It may be better in the long run to get a tame plumber in.


Hth

Again - Haven't done much on Ariston's - not many people install them or would buy them as they haven't got a great reputation.

If you have to remove the diverter to change the diaphragm, then you will need to isolate the electric and cold water supply, open hot taps and drain the heating section of the boiler, if you can access the diaphragm without removing the diverter from the boiler then you may just have to isolate the electric and cold water and open the hot taps.

Protecting yourself from electrics (electric shocks) and protecting electrical components from water (for damage and ££££££) are the main concerns, place a black bag and over the PCB, any water that escapes should run across the bag and onto the floor.

If you're unsure what to do - get someone in to do it for you - an RGI.

htg

Thanks for your help gents

I was able to access the diaphragm without removing the divertor valve, though it was fiddly. It did indeed have a split in it, which I have now repaired and all appears to be working as it should.

Hiya, in your servicing instructions it comes under "removing the main circuit flow switch"

part number: 571547
GC no: E24 077
probably less than a fiver for the diaphram.

isolate the boiler at all valves under the boiler and make sure you turn it off at the electricity supply!!!!!. Drain the boiler itself using the cock the manufacturer built into the boiler pipework, using a piece of hose into a bucket. Unscrew the diverter switch in accordance with your instructions (page 12 in my copy, Fig 1.40, 1.41). Usually the electrics fall into a convenient place to get completely soaked from the water in the switch so make sure you put a towel or a bin liner over the PCB. replace the diaphram and put all parts back together. Open isos and turn back on, you may need to purge the system of a bit of air but that is not always needed.

If at any point when reading this you feel uncomfortable get in a RGI.