isar 30 dhw problem

[Runninghotandcold]

Hi, My daughter has an isar 30 and over a period of a few months the temparature of the dhw is gradually getting cooler. If the kitchen tap is run at a low flow the water temp is too hot to put your hand in, but as soon as the flow rate is increased the temp. drops to almost cold.
I've read some of the feedback re. the diverter valve, the valve is moving and the c/h pipes do not get warm when drawing dhw. Is it likely the heat exchanger is the culprit? There are no fault codes displayed when the water runs cold. Any suggestions would be welcome, thanks.

 

[Ray84]

when you say if you running it faster it runs cold how much water are you drawing? do you have a water meter you could check or cut a 2litre plastic bottle and see how many times it can be filled in a minute?
it could be as you said a blocked heat exchanger but id guess its just down to the outside cold main temperature justnow, but at least youve proved the faults not with the diverter valve

Ray

 

[Runninghotandcold]

Hello Ray, thanks for your reply, running the tap at about 9litre/min gives cool water, but that is well within the boiler spec. which should give a 35 deg C rise at 12litre/min. 2litres/min. gives hot water.

 

[Ray84]

ok so if your quite confident its under performing to be 100% sure you could do a gas rate on the boiler. would you be able to read how to do this?
if its under performing it could be down to a choked heatplate as youve said or faulty HW sensor

Ray

 

[Runninghotandcold]

I've seen some values for the sensor but can't find them now. Do you know what I should be expecting to see, as I would like to rule out as many things as poss. before draining the boiler.