BM2000 intermittent hot water, DHWpump

Hi,
I have intermittent DHW from my BM2000, I have replaced both sensors but the problem persists.
I have been advised by the Gledhill helpline that the DHW pump needs to be replaced as the pump resistance is 209ohms. I am unsure about this though because the same pump is used for the boiler and CH and these pumps are reading circa 209ohms as well.
I have also noticed that when the hot water goes cold it is because the voltage supply to the DHW pump drops to zero volts.
Is it possible that with the higher pump resistance the pump runs slower and times out? I don't want to buy a new pump if the issue is the ACB.

any advise apprecited

You could swop the Pumps and check if this makes any different ( course the original Pumps are all the same model), if not, new PCB ( or refurbished, if you are willing to risk for a lower expense).
all depending on if your BM2000 has switch or not ( electric backup boiler ) With switch!: this could be also the switch pcb ( the one behind the silver nop on the front panel)
On the switch model , the DHW pump is activated via the switch pcb , not from the main pcb ( check the electrical diagram for this!)
hope this helps
regards Mario at Mario's Boiler Service

Thanks for the response,
I have tried swapping the pumps, although they all have the same resistance reading anyway.
I do have the switch model so the smaller circuit board may be a option, I hope its not the ACB as that will be a bit pricey.
The frequency that the water temperature fluctuates at is very precise almost like its some kind of internal timer issue.
Does anyone know if this could be anything other than the ACB?

Check the sensors.If you have zero voltage to the pump.
Then it is not the pump at that moment.
Does the ACB appear normal?
The sensors tell the ACB etc which then operates the pump speed for DHW temperature.
There is also below the pump a check valve.I have had these stick.
Also check all connections too.
As in pump
ACB etc etc.
Mike

Hi Mike,
Thanks for the reply.
I have replaced the sensors, (originally noticed fluctuations on PHE sensor but replaced both) I have also verified the reading that they are giving with a external temperature probe.
The reading given on the ACB display corresponds to what my external probe is saying.
Like you suggested I have checked all of the connections and have found nothing.

So after another call to Gledhill technical helpline (60 pence per min ffs) I have again been told that it is the pump that needs to be replaced.
The way that is was explained was that the higher resistance in the pump can cause the pump to draw too much current from the ACB which can cause the pump voltage to cut out. This seems plausible to me but I would be interested to hear what others think.

Have you checked the store temperature?
And as a matter of interest;
Checked the F7 E tank?
Checked the unit will take water?
Mike

store temp @72deg
F&E Tank has water
Unit takes water, I drained down to allow DHW sensor change and it re-filled without any problems.

Well if you have changed the pumps round it does seem odd to say the pump.
What about checking the check valve in the brass housing between bottom pump valve and pump?
I have had them stick before as in open only after 5 attempts etc.
Only plastic with a spring.
Mike

OK it's fixed.......
I had a look at the check valve and all was OK so I ordered a new pump, tested the pump resistance and had 175ohms so was really hopeful that this would cure the fault...no such luck, new pump made no difference.
So I removed the PHE and found it to be quite badly scaled, ordered and fitted a new PHE and the problem is finally fixed.

I did not notice any loss in water pressure on the DHW but we do have very good water pressure, I couldn't even notice any major difference between the hot and cold taps but when you blow through the old PHE you can notice a big difference between the two circuits..

I called Gledhill back because I wanted to have a bit of a moan about being advised that it was the pump, they then said that if the pump or PHE become less efficient the control system will cause the DHW pump to switch on and off, which then causes the pulsing hot water.
Apparently is does this as a result of not seeing the temperature changes that it is expecting.
I can understand their point about temperature changes but still think that they were very quick to get to the original pump diagnosis.
Starting to think that they have a vested interest in pump sales :-(

But at least I now have reliable hot water!