Buzzing DHW pump and PHE sensor error

Hi I am new to this site but have been visiting for a while. What a great site with lots of good info.

I have recently move into my house and as a result inherited this system (System mate 2000). I like the system over all as great for hot water at main pressure and constant heat on demand.

Haven't touch the system until recently had a problem where the heating stopped working the Boiler kept cutting out with over heat error. Turned out to be the pump. The pump was replace and all worked fine, however in changing the pump started to have problems with leaks at the isolation point on the pump, so got these all change while system was drained and notice DHW pump was not running. By the state of it looks like for a while too. Not really had any problems with hot water since moved in but couldn't run two showers at the same time. I didn't think anything of it at the time, just thought it was limitations of the system, but have recently learnt this is not the case. I am assuming the pump had been my issue all along then. Though the water stays piping hot throughout if only one tap or shower is used.

We changed the pump anyway, but now all the pump does is buzz and doesn't rotate. Checked the voltage and it is around 130volts all the time. The pump never turns off either, unless I reset the system. It then turns on the first time the taps are turned on and then remains buzzing, never to go off again.

I have since done a diagnostic test and get an error after pressing SW2 twice which shows an error on the PHE sensor. (oERR). Before I go changing this have a couple of questions.

The pump not turning and only buzzing, could this be related to the sensor error or is this another issue, possibly the control board? The pump runs fine in emergency mode on full speed, so pump is fine.

Is the pump varied in speed and could the sensor be causing the control board to drop the voltage if so.

Should I change both sensors and could I have a possible control board issue.


Sorry for all the questions and the long post. Any help would be much appreciated.

yes this is the sensor problem, and yes I would fit both sensors new, the bussing is from the pcb getting error from the sensor, and also yes the pump is running a different voltage, this is correct.
Mario at Mario's boiler service

Hi Mario,

Thanks for the reply. The pump is where the buzzing is coming from, like its trying to turn but not enough voltage. I'll check if the Control board is buzzing too. Hopefully changing the sensor will fix the pump voltage too.

Hi,

Just read another warning post on here about using the standard Grundfos 15/50 pump and how it shouldn't be used on the DHW side as it can't regulate the speed. The one fitted on the system should be capable at running to voltages as low as 50 - 60 volts. Have I understood that to be correct as that could also be the issue here.

The pump wont spin at 130 volts. Have I got the wrong pump and where can I get the correct one?

Lucky_s wrote:Hi,

Just read another warning post on here about using the standard Grundfos 15/15 pump and how it shouldn't be used on the DHW side as it can't regulate the speed. The one fitted on the system should be capable at running to voltages as low as 50 - 60 volts. Have I understood that to be correct as that could also be the issue here.

The pump wont spin at 130 volts. Have I got the wrong pump and where can I get the correct one?

yes that's correct
pumps you find at http://shop.segel.co.uk/
but try the sensors first

Can anyone point me to the correct pump as I can't find one anywhere.
I tried the link above and they don't seem to have any different pumps to the Grundof 15/50
Currently have a 15/50 installed but not spinning at 130volts. The one I replaced was also a 15/50 but was silver, so probably original equipment.