Potterton Heatmax combi 28 HE strange DHW issue

[RobertLeigh]

I have a Potterton Heatmax combi 28 HE that goes through short 5 sec cycles of the burner being lit then shutting off when using DHW. The CH works fine. The DHW is being tested with a single hot tap (not a mixer). The short spurts of burning is just enough to produce luke warm water. I understand a clogged plate heat exchanger is a common cause of this problem but in my case these on/off cycles start whilst the DHW heat and other sensors are still cold. There are no error codes. I've tried a new DHW NTC sensor. I'm suspecting an electronics fault, would like to be sure before buying new PCB.

Any advice appreciated.

 

[sugarlips]

it could possibly be the water flow turbine scaled up, a quick check is to turn hot water on and look at the red light on top of the sensor, if it is not a solid red but but you can see it flashing then its scaled up and needs changing.

 

[HERTS P&D]

Hey Sugarlips, where you been?

Andy

 

[RobertLeigh]

it could possibly be the water flow turbine scaled up, a quick check is to turn hot water on and look at the red light on top of the sensor, if it is not a solid red but but you can see it flashing then its scaled up and needs changing.

Thank you. I checked the light as you advised (mine is a hall effect sensor) and it stays solid red, so that's narrowed the 'possible fault' list a bit further. I'll report back when I finally find the issue, it's looking like the PCB.