Ariston eurocombi SX 20 - firing problem

25 Sep 2006
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United Kingdom
My combi boiler won't light to produce hot water unless the CH is turned on. When CH is off, turning on hot water tap does nothing at all to the boiler except make water flow.

That is a more recent problem but for the 2 years I've lived in this (1 -bed) flat, there's been a general problem with the boiler firing, e.g. on CH it has to take several attempts to light before it finally seems to catch and gas starts burning.

The diverter valve was replaced about 9 months ago (to fix a different problem) and it also got a service, costing £400 all up. The main power switch also had to get bypassed some time ago when it stopped working.

My question is - are the current problems a fairly simple fix or should I stop throwing good money after bad and stump up for a new boiler? I'm worried it won't make it through another winter.

The CH works OK (other than the annoying sound of the boiler always trying to light) and hot water is hot, flow rate ordinary.

Any help most welcome, thanks for reading.

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That was an expensive repair at £400 !

The current problem sounds like a diverter valve failure. Perhaps it was not really changed?

As you have not bothered to get it serviced for two years the failure to ignite reliably and may just be a need for cleaning.

The bypassed switch just needs a replacement about £8 for the part. If water has leaked onto it then the leak needs fixing first.

Its a quite fixable boiler and I would be surprised if it would come to more than £120-£200 at our prices but if you choose cowboys there is no limit to what you could pay.

Thanks for the reply.

I remember now that the diverter valve repair did fix something - the problem had been when DHW was turned on, the boiler ignited ok but heated the CH instead. At least that's what the engineer said and he pointed me to the hot CH pipe to prove it (are the CH pipes normally the thicker ones?).

I must admit that over time the boiler has gradually found it harder to ignite properly so perhaps a clean is needed. However, the service I apparently got 9 months ago did nothing to improve ignition performance. The engineer suggested it was maybe a switch or board problem.

Could this problem of no DHW unless CH is on be anything other than diverter valve?

Thanks again.
It could be almost anything!

Its usually the diverter valve but it would need a competent boiler engineer to correctly diagnose the fault.

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Be aware that there's a diaphragm, cheap and easy to change, in the Diverter valve, which is less so as a whole. The most common failure is the diaphragm, but the part it pushes in the DV body has to move, completely, without sticking.

The poor lighting is usually an air flow problem (part about £40 iirc), and those ARE unreliable mains switches.

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