Boilermate OV A-Class - Boiler Pump is always ON

wecandoit · 8 Nov 2010

Hello,

I have Boilermate OV A-Class installed at home that we have recently moved in. I have realised boiler pump is allways on (i.e. boilermate's hot water function demands heat always). When I have opened up the boiler and checked the circuit board I have realised Middle sensor set to 75C for OFF. And When I have checked stored water temperature, it can reach max of 73C (this is with max setting at boiler). So due to heat loss etc. stored water cannot reach max temperature required by Boilermate which results in constant heat demand from boiler. Easy solution for me is to be able to reprogram the Middle sensor set point to a lower value (e.g. 72C) but I do not know if I can do it.
I appreciate if you know how to do it.

P.S. I am an electronics engineer and I might be able to reprogram IC on the board if I can find out data locations.

Many thanks.

wecandoit · 8 Nov 2010

Here is an idea:

I think midpoint sensor is NTC so I need to add a resistor in parallel to make PCB think that stored wtare temperature is more hot. I need to measure NTC resistor to gind out its spec then add a potentiometer to tweak the value then I can add fixed resistor!

seco services · 8 Nov 2010

thats ok if you understand that.

petit_pablo · 8 Nov 2010

Easier solution is turn the boiler stat up. The boiler needs to be run on max with a thermal store.

wecandoit · 8 Nov 2010

Thanks for the reply. Unfortunately, Boiler is already at max!

petit_pablo · 8 Nov 2010

Then it should be getting the store up to temperature.

How have you tested the temp of the store?

wecandoit · 8 Nov 2010

On the PCB there are two push buttons and you can go through all the sensor readins as well as set points. There is a 7 segment two digit display which shows the values.
Thanks

wecandoit · 8 Nov 2010

I wonder if I reduce the boiler pump speed Do I get temperature increase due to the fact that water will spend more time in the boiler while heated! Pump is at max speed currently!

petit_pablo · 8 Nov 2010

You need to know how hot the boiler flow is first.

Do you have any form of temperature sensor? What boiler is it anyway?

wecandoit · 8 Nov 2010

It is baxi solo (I think 30). I have temperature sensor (thermocouples with copper pads plugs into reader)

petit_pablo · 8 Nov 2010

That will do me.

Boiler flow should get above 75deg on max.

wecandoit · 8 Nov 2010

Thanks. I guess this is the issue! It is reaching maybe just above 75 and with a loss on the long pipe etc from boiler to boilermate it never can make store temperature of the system above 75 which is required by sensor!

petit_pablo · 8 Nov 2010

Sounds like it. You may be able to improve the boiler flow temp by having the thermistor and potentiometer on the boiler replaced.

It may be that this sytem has always been like this from new however.

wecandoit · 8 Nov 2010

Thanks for your time. Yes you are right I have seen an installation report and it says max store temp can be achieved is 70C. And whoever installed the system did not understand much about Boilermates requirements (although it is in the installation instructions). Anyway I will measure flow temp first via thermocouple then get the parts that you have suggested replaced and hopefully get some result! Many thanks.

ColinJacobson · 8 Nov 2010

petit_pablo said:
Sounds like it. You may be able to improve the boiler flow temp by having the thermistor and potentiometer on the boiler replaced.

It may be that this sytem has always been like this from new however.

Try insulating the flow pipe from the boiler and reducing the pump speed. Of course test if the boiler can get to 80C first.

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Boilermate OV A-Class - Boiler Pump is always ON

ColinJacobson

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