Ideal Isar HE24 hot water woes

I'm at a bit of a loss here and need some advice. I know they're terrible boilers, it was in when we bought the house and it's been trouble free for 5 years, it's now showing it's age and being a right pain.

As I say it's been absolutely fine up until a month ago when it stopped supplying hot water at full demand. Half-way you'd get just hot enough, the shower wasn't great, it would go hot-warm-lukewarm in a little cycle. We got someone out and he changed the diverter valve, and unfortunately it didn't make a hell of a lot of difference - the CH flow pipe gets hot when a hot tap is on but the diverter is operating, you can hear it and the display goes to 'd'. Ideal suggested it could be a blockage, so we had a power flush done, this has improved the heat coming from the radiators and the hot water at full demand was back... for a few hours! It's now worse than it was before.

Now it fires up when you turn it on, the CH (as before) works perfectly. The DHW, when it fires up and 't' is displayed - if you run a hot tap you'll get a few seconds of lovely hot water, but when it flicks over to 'd' the boiler will show that the burner is on for about a minute or so, the water goes to freezing cold and the burner light goes off. If you leave the tap open after the burner light has gone off, it'll start flashing L9 - I believe this is either a blockage or the thermistor according to the manual, but I've seen mention of it possibly relating to the pump. A little earlier I ran the hot tap and felt the CH flow pipe and it was warm, DHW outlet was very cold.

When the power flush was being done, I asked the engineer how bad the water was and he told me it was pretty clean, a lot better than he was expecting.

I spoke to the heating engineer yesterday on the phone and told him what was happening and as all things still pointed to a blockage, he recommended I contacted the power flush company as there must still be debris and they are saying that there can't be a blockage as the system was clear.

At the moment I've got it switched off as I don't know what to do.

Does anyone have any ideas what this could be? I feel a bit in the middle here, if we get someone out to clear a blockage from the heat exchanger or replace it, is it just going to block up again and we're back where we started? Could it be the diverter?

We've already spent £350 to get to this point. I'm considering just binning the thing and getting another boiler, but I don't even know what a good replacement would be. I've heard Intergas boilers are good for systems like ours as they can't block up in the same way.

Any recommendations on possible replacements and rough costs would be welcome, the evil not-Ideal is in a kitchen cupboard at the moment so wouldn't want one massively bigger.

Thanks for reading

You need a new plate heat exchanger and a new diverter valve cartridge. Not particularly expensive or hard to fit.

So you have had a trouble free 5 years and now it's a terrible boiler

shambolic said:

You need a new plate heat exchanger and a new diverter valve cartridge. Not particularly expensive or hard to fit.

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Thank you, the diverter cartridge was changed less than a month ago, could this be a dodgy part?

This morning it's giving a bit of hot water again, on half-way it's hot-warm-lukewarm, but it's still firing the burner for a minute then off again and it doesn't seem to re-fire but not going to L9 as it was yesterday. I just wish it was consistent!

danfre said:

So you have had a trouble free 5 years and now it's a terrible boiler

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Well when you put it like that it's been okay for us, but it's not the boiler you'd choose! I think I've read most of the posts on the internet about them and they don't exactly have a stellar reputation!

I personally think that preheat/warmstart call it what you will has got a lot to answer for, unfortunately you have it on the Isar but it cant be switched off, prolonged use of it causes problems with plate heat exchangers scaleing up in hard water area's, changing it isn't too difficult for an engineer as its the smaller 24 model.

heatservice said:

I personally think that preheat/warmstart call it what you will has got a lot to answer for, unfortunately you have it on the Isar but it cant be switched off, prolonged use of it causes problems with plate heat exchangers scaleing up in hard water area's, changing it isn't too difficult for an engineer as its the smaller 24 model.

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We're in a soft water area, scale could be an issue but magnetite was present (small amount) in the pipe when it was drained for the diverter cartridge change. That's why we had the power flush done.

I've done some more research this morning and there's a suggestion that this could be an air lock... absolute nonsense or possibility? Water is coming out from the hot taps, but is going cold on full demand, will go back to hot-ish half-way. No more L9 flashing. It's not making any weird noises, but I did have some hissing last week, but that was making the pressure gauge fluctuate and then it would go into L9 flashing.

This boiler is driving me mad cos I need to figure it out

If heating ok then it’s plate heat exchanger. Pump not working would L9 on heat and hw.
Also have you took head off diverter and pushed spring in and made sure it comes out immediately fully?
They stick with black crap drying out grease quite quickly.

Power flush carried out with boiler connected will push dirt into plate. Power flush also won’t clear plate unless diverter put in hw mode and system then isolated to just clean hot water (boiler side) circuit.

shambolic said:

If heating ok then it’s plate heat exchanger. Pump not working would L9 on heat and hw.
Also have you took head off diverter and pushed spring in and made sure it comes out immediately fully?
They stick with black crap drying out grease quite quickly.

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The engineer was testing that when he was here and the diverter was not sticking, and I'm now familiar with the noise it makes when it switches. The heating is absolutely fine and always has been, the issues we've got are all DHW. My partner has just been in the shower and it was lukewarm, I checked the pipes under the boiler and the CH Flow pipe was cold and the DHW outlet was hot. Which is different to what it was doing even yesterday!

shambolic said:

Power flush carried out with boiler connected will push dirt into plate. Power flush also won’t clear plate unless diverter put in hw mode and system then isolated to just clean hot water (boiler side) circuit.

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I did tell the guy who did the flush that the problems were in the boiler, it was connected up to the boiler but I have no idea if he did anything specific, he did run the hot tap in the kitchen for a while. As you can tell, I have no idea about this sort of stuff!

Thanks again, all seems to be pointing back to the heat exchanger! There aren't any noises like there's steam in there, the 'kettling', I think I've read too many forum posts for my own good!

Not main heat exchanger as that’s £600 it’s the plate heat exchanger purely for hw. Noise from diverter means nothing as it springs open for hot water and doesn’t make a noise. It motors closed on heating.
But if flow not heating up then diverter ok.

Is this the part? https://www.ebay.co.uk/i/272864265285

On parts sites it seems to be £100+ so dubious about that!

claicham said:

Is this the part? https://www.ebay.co.uk/i/272864265285

On parts sites it seems to be £100+ so dubious about that!

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Yes depending on model and serial number though as there are about 8 different ones for Isars

Thanks for all your help. Had a chat with my other half tonight and whilst it might be a relatively cheap fix for the heat exchanger, we’re going to go with the new boiler as he’s sick of me going on about this one, I guess as it’s being ripped off the wall I can autopsy it and find out exactly what was wrong!

I’m looking at the Intergas compact eco 24 as it’s replacement. Good warranty and reviews look excellent.

Get rid of that pile of crap , one the worst boilers going.

The auto air vent are prone to scale up and not work, only thing is it located in the boilers balanced compartment behind the flue on the R/H side and you need a GSR engineer to check it.