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Updated 01 November 2020   Boiler Services Ltd 2009-2020

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Vokera Mynute 14SE Gas Boiler Faults, Problems and Fault Finding

Vokera Mynute 14SE boiler not firing consistently and making strange noises

When we arrived we found the boiler had stopped working completely. We could hear the pump running so we eliminated the possibility of a blown fuse in the main isolating switch for the heating circuit.

The Vokera Mynute SE boilers are automatic ignition system boilers for central heating. They incorporate a circulating pump, expansion vessel, safety valve, pressure gauge and automatic bypass.

This boiler uses a flow switch to prove pump operation before initiating the ignition sequence so we visually checked the operation of the flow switch. The push rod in the differential pressure unit is out when the pump is not running and retracts when the pump runs. We found the push rod didn't move at all on pump speeds 1 or 2 and was not consistent even on pump speed 3 though when it retracted the boiler fired normally…

We rang Vokera Tech Services (08703 330220) to ask if there was any was to distinguish between a diaphragm fault (in the differential pressure unit) or a pump fault (worn pump providing insufficient pressure).

Tech Services said we could check by removing the access plug at the end of the pump spindle (Grundfos 15.50 circulating pump) and trying to stop the spindle rotation using a large flat bladed screwdriver. He said it should not be possible if the pump was OK (the pump was set on speed 3). If the pump was OK we should suspect the diaphragm in the differential pressure unit or, possibly, a blockage in the differential pressure unit.

Since this was a system boiler working at 1 bar pressure, this check didn't work for us as slackening the access plug released too much water (by now hot water) above the live electrics. The electrics would have to be live to run the pump.

With the boiler running, the entire radiator system had got evenly hot so the pump was an unlikely culprit and in a 9 year old boiler the flow switch diaphragm was quite likely. We changed the diaphragm in the pressure differential unit (it was perished and perforated) and resolved the intermittent problem.

In the Installation and Servicing Instructions for the Vokera Mynute 14SE the flow switch diaphragm was Part No. 0557

The instructions also say that if a replacement pump head is required, the head from a standard Grundfos 15.50 pump should be used.

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