ideal isar he24 combi boiler fault

6 Oct 2008
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United Kingdom
i have a ideal isar he24 condensing combi boiler with a heating fault.
the hot water is fine- no problems. but when the heating is due to come on the 'c' appears in the window but the light just flashes, there are no fault codes and the water pressure is set to 1 bar as stated in the book,
Please, can anyone suggest a cure.
Paul :(
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Thats a new one!

Does it just carry on doing that for 30 minutes if you leave it?

Apart from a pcb ( expensive ) then I would have expected that any normal fault would generate a fault code after a few seconds.

I presume that the boiler does not start the pump or make any noises?

Have you checked to see if its still under the warrantee?

if you reset the boiler by turning off the main supply
(breaker) the boiler will start ( i hear sounds) the light flashes quikly then after about 15 seconds the sounds stop and the light flashes slower. the light flashes for as long as you want to watch it. as soon as the hot water is turned on c changes to d the light flashes quickly then light stays on, on turning off the tap it changes back to a c then flashes quickly for 15 seconds then slowly again.
It sounds as if the gas mixture will not support combustion at the ( lower ) heating power setting.

I would be checking the gas pressures but then I am registered for gas work.

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It sounds like you have a dripping tap or small water leak on the hot supply. If you isolate the cold water to the boiler ( underneath, flat bladed driver, quarter turn clockwise ) this will normally fire the CH if it is being called for via the programmer and roomstat.
Whilst that would prevent the CH from working it would also give a "d" in the display because it thought there was a DHW demand.

It would also annoyingly cycle on/off every few minutes.

Consequently as the OP has not mentioned either of those malfunctions I would not expect that the be the problem in this case.

But apart from a gas mixture problem I cannot think of anything else at the moment.

I must get new glasses Tony :rolleyes: - of course 'd' flashing would be dripping tap etc. It could be circulation problems, eg pump, system contamination or possibly the diverter sticking.
Does the boiler fire at all for CH ?
the boiler will fire momentarily if the system has been reset by using the breaker on the consumer supply
Normally, if the pump or heat exchanger were faulty, then a fault code H9 or L9 would appear. As it appears not to be the case are you confident / competent to remove the outer casing and check the diverter valve?
I would be inclined to ask a RGI to investigate, unless the boiler is under 2 years old whereby it would still be under guarantee.
Flashing light is either boiler up to temp and shut off on its own stat or boiler on pump over run.

As your boiler has not fired for ch, I doubt it is up to temp.

Check the resistances on the ntc are within the range set out in the manual.

Unfortunately there is more chance of winning the lottery than an Ideal boiler giving a correct and meaningful fault code :rolleyes:
Have you got an external thermostat ?Check this if you have, and is the internal stat (on the boiler) turned all the way up.
As your boiler has not fired for ch, I doubt it is up to temp.

But it could be after the DHW preheat has kept the plate up to temperature and the diverter valve has not moved!

I would then advance my suggestion about the gas mixture to a probably stuck diverter valve.

This is particularly likely as stuck diverter valves have always been a common fault on these series of boilers.

If there is a little white lever on the side of the diverter valve motor see if it moves between DHW and CH.

Even if it does move the pin is probably stuck down!

ill check the diverter valve tomorrow when i get back.
ill let you all know what happens.

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