Ideal Isar hot water issue

[AllyBongo]

My Dads been having trouble with his Isar M30100 for a few months now. First time I've worked on one of these, as I know there reputation! If its an easy fix I will sort it, if not its new boiler time. As i dont have a great deal of experience with these, I'm looking for some advice.

CH works fine, when the DHW is running, it runs for approx 30 secs then cuts back to low burner, stays at that for a bit then back to high, and carries on like this. I suspected the DHW thermistor, but at £35 from Partscenter its not a cheap trial and error. Resistance was hard to take, with the water running, but at its hottest setting it was around 8-9kohms.

Also the heat it passing down the flow a bit, and the inlet pressure is only 12mbar (Gas pipe is 15mm from the meter, about 12-14m of pipework) But I didn't think these issues would cause the burner to go to low.

Any help appreciated folks

 

[Ermintrude]

Diverter/ water turbine and clean out plate. Then sort out gas.

 

[arran197]

If you test the resistance on the thermistor when cold, you don't need the water running. It should be 16 ohms there or there abouts. You need to sort out that gas pressure issue though. Check the meter outlet pressure too as that might be too low. I would start off with that and I'd have a look at the plate heat exchanger, you might need need some new rubber washers, but other than that, cleaning it out won't cost much.

 

[newcastle phill]

Theres the thermistor chart

 

[Millsy 82]

If it's going onto min flame then I would rule out a blocked/scaled phex. (Most usually cut off if it's a blocked phex) I don't think these have a flow valve as it's all done off the thermistor (I could be wrong on the older ones). If the heating is working then I would say pump is ok. Only really leaves Pcb and thermistor.

Me personally I would say rip it out as for an isar it's had a good life.