Hot water problem and pump resistances

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Hot water problem and pump resistances

Post  Stevvo on Tue Jan 15, 2013 12:29 pm

I was asked to repair a 2000 model after the householder had a bash and left it leaking!

The hot water delivery is a bit random temperaturewise. I called the Gledhill tech helpline and the guy at Gledhill asked me to read all the values on the pcb display which were showing ok. He then asked me to 'wiggle' the sensor wires on both sensors near the plate heat exchanger. As the temperature readings were ok and didn't wildly fluctuate when 'wiggling', he says the sensors are ok. He then asked me to power down the unit and take a resistance across live and neutral on the dhw pump, with the pump set on speed 3. It read 250 ohms, so I am told the pump is no good and need replacing. He told me the pump should have a resistance of 175 ohms and this will resolve the problem.

Now I'm not totally convinced and a new pump will be expensive. The reason I'm not convinced is that the householder lives on an estate that suffered flooding a few years back and many of the Gledhill 2000's were removed. He robbed 7 pumps! (and many circuit boards too) and not one of these spare pumps gives this resistance reading. They are all reading 209 upwards on speed 3.

Has anyone got any idea whether it could be the pump or something else causing the irregular hot water temperature. The plate heat exchanger is not furred up btw.

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Re: Hot water problem and pump resistances

Post  mike on Thu Jan 17, 2013 11:40 am

Just a thought. Is it are they the correct pumps?
Mike

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Re: Hot water problem and pump resistances

Post  Stevvo on Thu Jan 24, 2013 5:27 pm

Hi Mike, Thanks for the reply. The pumps were from identical models in neighbouring properties. Anyway I now have the unit operating correctly once more. I brought along both a pump (as advised by Gledhill tech) and a DHW sensor. Before I did anything I tested the resistance of my new pump which was curiously 209 ohms (more or less the same as the pump, Gledhill advised me 'knacked'!) .

Because of this my hunch was to replace the sensor, which I did and now the hot water is working satisfactorily.

I still have a question regarding the pumps though. Are all three modulating pumps? They all appear to be identically labelled and there only seems to be one order number for replacement pumps (apart from the 15/60 pump required on larger models). I'm struggling to see a need for the boiler pump to modulate. Surely this just needs to get heat into the store as quickly as possible?

Is there any way or point in reading the resistance of a sensor. Both the old sensor and new replacement simply gave me a 1 reading on my meter?

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Re: Hot water problem and pump resistances

Post  mike on Thu Jan 24, 2013 5:34 pm

You will find very often when the units are made by Gledhill.
They will fit the DHW pump to the DHW, The boiler pump and the heating pump (say BM 2000)
That is fine.
When replacing you can fit
Any 15/50 0r 15/60 (bigger units.)
To The boiler pump
The heating pump.
All they did when making the unit fitted the DHW pump to all 3 location.
That is fine as the pump will run at those voltages required by the boiler and heating pumps.
But the DHW pump does run at a lower voltage when required by the sensors / ACB.
And the normal 15/50 pumps will not do that.
Confusing but that why.
Mike
MGC/H2O
Norwich.

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Re: Hot water problem and pump resistances

Post  Stevvo on Thu Jan 24, 2013 5:45 pm

Thanks for your assistance. We only have one small estate in town that uses these units and I'm getting the reputation as the 'expert' (dear me!). Not scared to have a go, these are not my most profitable jobs.

You should prduce a book Mike and make some money from your knowledge.

Any ideas on the sensor resistance question I posed?

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Re: Hot water problem and pump resistances

Post  mike on Fri Jan 25, 2013 11:51 am

British Gas reckon they test the Gledhill sensors.
But Gledhill have told me that you can not test them.
Mike

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Re: Hot water problem and pump resistances

Post  Stevvo on Fri Jan 25, 2013 1:54 pm

Thanks for your help.

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