DHW Pump Runs Constantly

Hi All
I have an issue with the DHW pump (running the heat store through the heat exchanger) running constantly on my Boilermate 2000. This only happens when the store temperature is below around 45 degrees (not sure of the exact temperature, but it's there or thereabouts).
This is only really a problem during the summer months when I keep the store temperature low. During the winter when the C/H is running the store temperature is generally well above 45 degrees, with the boiler running for much of the day. However, during the summer months I only tend to do a 1 hour "boost" in the morning and that generally lasts the day. BUT, by late in the day the store temp has generally dropped to below 45 degrees. That's still plenty hot enough for our DHW requirements, but as soon as the hot tap is run for a few seconds, the DHW pump kicks in (as it should), but then continues running until the store temperature rises to above 50 degrees (approx) or until the system is power cycled and the board resets.
I did raise this issue on the forum before and I was told it was probably the PCB, but that was changed a while ago and the new one does exactly the same thing. Is there any way of "fooling" the system into thinking it has enough heat in the store to kill the pump overrun? I'm an electronics engineer by trade, so quite happy to fiddle around with the PCB if there's a workable solution. I've thought of adding a timer to power cycle the system every 30 to 60 minutes, so the board resets periodically and the pump stays off until the next time the hot tap is run, but there must be a more elegant solution?
Cheers for any thoughts.
Mike

Hi
BM 2000 ?
If so your boiler should be on MAX to heat the store to around 75 / 77c
When satisfied your boiler will stop.
I would think you are running your boiler on a low setting.
Therefore you will use more gas or oil or what ever.
Boiler needs to be putting out 80c to satisfy the BM 2000.
That is the design of a Thermal store .

Mike

Hi Mike

Many thanks for the prompt reply. The boiler is on MAX and during the winter there is no issue, but during the summer months we EITHER only turn on the boiler once a day for a quick boost (say 40 mins), OR, as I also have solar panels installed, I let them heat the store. Why would I want to waste oil heating and maintaining a full tank to say 75 degrees when a store temp of around 45 degrees is ample for our daily needs, and a quick boost or a few hours of sunshine can achieve that. The PROBLEM, which I presumably failed to explain very well is that at 45 degrees the DHW pump runs indefinitely once triggered by the flow sensor. In all other ways the system works fine.

I hope that helps to explain my issue? All I want to do is to "fool" the system into switching off the pump as it would do if the store was at 75 degrees.

Thanks
Mike

I think as Mike has already alluded to the issue is that you are trying to run the system outside the design parameters. The system will try to keep the plate heat exchanger (PHE - DHW) at a temperature that is able to instantly address a hot tap being turned on. As there are no user settings to tweak on the control board I think the best you can do is up the output temperature on the boiler until you hit a point where the plate heat exchanger thermistor is happy that the PHE is at a sufficiently high temperature to turn off the PHE (DHW) pump. Given the higher ambient air temperature in summer and the subsequent reduction in heat loss from the store etc. I would wonder what sort of saving might be made by turning the boiler down, I guess you can judge this from your bills. Just by way of illustration when the system is fired up from cold once the store has sufficient heat in it the PHE pump will run at low speed to pre heat the PHE so that the system is ready to supply hot water, people often mention that the system buzzed for a while which is the pump running at low speed.
Regards Murray

I "cheated " the DHW pump temp. sensor with a plumbing fix - interrupted the pump lead via. a flow switch in the hot feed pipe to taps.It only runs when water flows to outlets.

I have my boilermate running using a timer that allows the system to heat 4 times per day. If the store temperature falls too low, it thinks the hot tap has been switched on and will then constantly run the pump, this sounds like what you are getting. It needs to be kept above 55c to prevent this.

Regards
Richard