Boilermate 2000 dhw pump overrun

Hi All

I'm hoping someone on here can help with a technical question.

I have a Boilermate 2000, which is heated by a boiler AND solar panels. The boiler side works fine all year, and the solar panels side works well during high summer. However, in spring & autumn the solar panels struggle to get the store up to temperature, BUT most of the time they still provide enough of a boost to keep the store temperature high enough for everyday use, without resorting to using the boiler.

The problem is the dhw pump. As you will know, the pump is set to kick in when a hot tap is opened to circulate the store through the heat exchanger. It is also programmed to overrun by 3 minutes or so after the tap is closed. HOWEVER, if the store temperature is low, eg 40 to 50 degrees C (which is still OK for dhw use) the dhw pump just stays on, forever! The Boilermate is probably calling for heat from the boiler at this point, but because I have the boiler switched off the store temperature remains constant and the pump stays on.

I have an electronics background, so I'm not frightened of adding a timer circuit, relays or whatever to fool the system into thinking that there is sufficient heat. If I'm honest, I don't really see the point of the endless overrun anyway. Why doesn't the pump just shut down and restart when the next tap is opened - is the pump controlled by temperature differential and not by a flow switch maybe??

Any advice appreciated.

Thanks
Mike

Hi Mike
Yes the DHW Pump is started and stopped from temperature differential between the two sensor on the exchanger, not from a flow switch as in the mark 2 and first of the mark 3 version of the Boilermate. If ,after the hot water run, the Temperature is not coming back to 55c on the top sensor the pump will run about 10 to 15 minutes, depending on the software version of the PCB. Is tricky to fit something to stop this overrun, except switching the Boilermate of and back on again. On a caravan would be simpler, course the tap activates the Pump via a switch in the tap, but this didn't help with your problem. Sorry
kind regards Mario at Mario's Boiler Service

Hi Mario

Many thanks - at least I now understand how it operates. However, you say the pump runs for 10-15 minutes on overrun - I could live with that, but mine runs constantly, all day and all night!

Do you know which of the sensors is looking for 55 degrees (ie main store, heat exchanger or dhw sensor?) I could maybe add a circuit to temporarily fool it into thinking the temperature had hit that level?

Thanks
Mike

baggy99 wrote:Hi Mario

Many thanks - at least I now understand how it operates.  However, you say the pump runs for 10-15 minutes on overrun - I could live with that, but mine runs constantly, all day and all night!

Do you know which of the sensors is looking for 55 degrees (ie main store, heat exchanger or dhw sensor?)  I could maybe add a circuit to temporarily fool it into thinking the temperature had hit that level?

Thanks
Mike

Hi Mike
The sensor ,responsible for the Pump to go off, is the PHE return sensor ( page 22 in the manual / wiring diagram). How old is your Boilermate 2000, course there was software updates over the time and if you have the old software on your pcb, there could be a buck in the software version if yours is from the early models. This also could fix your problem. Cape me updated with the progress.
regards Mario

Hi Mario

Many thanks. The model has a manufacture date of 15/11/2002. Does that make it an early one? I would certainly say it was a software issue if the pump is meant to go off after 10-15 minutes.

I can have a play around with fooling the sensor into thinking it's seeing +55 degrees, but do you know how the sensors work? 3 wires is unusual if it's a standard thermistor. Is the third wire just an "earth"??

Cheers
Mike