IDEAL ISAR HE24 INTERMITTENT HOT WATER

[Siddiq675]

I have an ideal ISAR he24(yes I know it's terrible and I should get rid but I cannot afford a new boiler arm). The CH is working perfectly and the tap when turned on slow gives out hot water but when I turn the hot tap on faster, the water comes out lukewarm. The boiler still shows d and the burner lights but the water is just not hot enough.

I initially got a H3 fault a few days ago but the engineer came and changed a DHW THERMISTOR. This although I initially thought cured the problem actually didn't.

Any help in the right direction please and also what I should look for when the engineer comes out again?

 

[twgas]

Could be the diverter passing to rads when in HW mode, maybe the plate h/ex needs cleaning or replacing.

 

[shambolic]

What is the flow rate of the HW when cool. This boiler will only deliver a maximum of 35deg temperature rise at 10 litres a minute.
If cold coming in at 5 then you will get 40 at tap (lukewarm) not a fault. Does it get hot when run slower. If so then boiler is ok.

 

[Siddiq675]

Thanks for the advice.

I have placed my hand on the CH feed pipe out the boiler when system is cold and after turning on hot tap, the pipe does not get hot as some have suggested would happen with a diverter fault.

It gets hot when slower...when i run it faster, it almost always brings up the H3 error code after a min or so. Running it really slow just allows me to get a bit of hot water out to run a bath.

I have never had these issues before and have had this boiler for about 5 years so I don't believe its related to the flow/incoming temperature etc.

Whilst having this H3 fault, I have also got a LF code three times but this is ok once i reset it.

 

[shambolic]

H3 is dhw thermister.

 

[Siddiq675]

This has already been replaced by the engineer.i actually saw him change it for a new one.

 

[shambolic]

Any sign of water dripping onto wires at stat? If not then pcb or wiring faulty.

 

[Siddiq675]

The book and fault code does go along with your theory but it's just so many people including twgas have mentioned the diverter valve and DHW plat h/exchanger.

I hvae checked and the engineer also checked and there were no leaks whatsoever in the boiler.

As the fault is of the intermittent kind, it's hard to know what to change to rectify it. By the time I actually get to the correct part, it could cost hundreds.

 

[Siddiq675]

Just to let you all know that a new PCB cleared the H3 error code but water was stil intermittently going hot and cold.

Plate heat exchanger was cleaned out and I now have hot water back.

Thanks to all for your help.