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 Post subject: Baxi flowswitch problem
PostPosted: Thu Mar 09, 2017 6:52 pm 
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Thought I might share my experience of flow switch problems in a Baxi 100/2 He plus although I think this type of flowswitch is/was fitted to a number of conventional Baxi/Potterton boilers. It is a simple on/off switch, open circuit when the pump is off ie no flow and closes the circuit when flow is present. It has a paddle-magnet that operates a reed switch of some type embedded in the body.

About 4 years back I had a motorized valve failure where the valve closed (Danfoss) but the microswitch was still making a circuit, attempting to run the pump and the boiler but against a closed circuit ie no flow. Clearly the boiler flow switch should have prevented any attempt by the boiler to fire up, but it was heard knocking and banging (in the garage so prettty loud!) the thermostat seemingly kicking in each time it overheated because of no water flow. On checking the flowswitch with a meter it had a permanently closed circuit. I stripped it out (a bit awkward and be gentle on the o-rings!) and found it was jammed open by a build up of iron oxide particles stuck to the magnetic paddle. It can be dismantled for careful cleaning. I fitted an Altecnic (same make as the flowswitch coincidentally!) magnetic filter system to the return pipework as I did not fancy a repeat.

Anyway just had exactly the same thing happen again - boiler banging away last week one morning with the timer set to OFF - replaced the microswitch in the Danfoss motor valve and all ok. Cleaned out the magnetic filter on the boiler, some particles found but still 95% empty. Stripped out the flowswitch and hey.. jammed with particles again.... Frightening really.... Why a magnetic switch in an environment full of metal particles...???

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PostPosted: Sat Mar 18, 2017 12:27 am 
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Cheap and easy design.

Those magnetic particles were not the boiler makers but dirt which should not have been in the system.

Good riddance to the installer who did not clean the system to have to pay for all the subsequent repairs!

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