Pulsacoil A-class Circuit board

[SteveS]

I have a customer with a Pulsacoil A-class unit where the circuit board has failed. Pump does not start up when demend is present and the voltage applied to the relays is 40V. I have measured the resistance of the relay coils to be 4.66 mega ohms is this what would normally be expected?

If the pump has caused the PCB to fail how do I determine this by electrical tests?

I do not want to put another board in just to have it fail due to a pump problem.

There are three wires and an earth going to the pump - what does the wire marked up as "M" do, I imagine it controls the speed of the pump but how does it do it and what electrical measurements can be taken to ensure that it is OK.

Many thanks in anticipation.

Steve

[Mike the Boilerman]

Hi Steve,

The A-Class Pulsacoil circuit board is pretty robust. I have only ever seen one fail so far, and that was caused by heat damage when the power relay fitted immediately below it overheated and caught fire. Sensors are equally reliable so if no power to pump during demand I agree, must be board or sensors. I don't know how to establish which though. Best to ring the Gledhill tech support line and pay the 60p a minute!

Pumps only fail and take down the circuit board if they get water inside. Is there evidence of water leaking from the upper pump isolator valve spindle, and aluminium corrosion around the pump motor where the control box is attached? This is the usual cause of pump failure.

I still don't understand the four-wire Grundfos pumps on an A-Class myself yet. They are seriously expensive! An ex-Gledhill engineer told me the other day that a standard Grundfos 15/50 can be converted to four-wire but I haven't investigated properly yet.

Sorry not to be of more help.

Cheers, Mike

[SteveS]

Thanks Mike,

Changed the circuit board and all appears to be OK now.

Cheers Steve

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