On 22/11/2017 20:55, Cynic wrote:
I've got a friend who has a Firebird oil fired combi about 15 years old. It's been a reliable unit with the exception of suffering a few failures of the 1/2" flow switch that detects when a hot tap is opened and starts the pump feeding primary hot water to the plate heat exchanger.
There was a component change of type of switch from a microswitch to a reed type a few years ago accompanied by a slight circuit change so the reed switched the coil of an octal plug in relay. The paddle operated reed switches in a plastic body are prone to failure in the nc (on) state which results in the central heating pump being inhibited. I replaced one for her a few days ago and it's failed again already. It shows continuity in the on position but has a resistive path in the off position. I'm guessing it's got water in the internal (sealed) connections. Whatever the reason it's holding the relay energised.
I'd like to find a robust suitable 1/2" flow switch capable of switching a grundfos 15-60 and rated for mains cold water pressure, say 6 bar or more..
Anyone able to suggest a suitable make and model, economically priced and available in the UK?


I use one of these:

http://uk.farnell.com/gentech-intern...-bf9f-00001000

but it might well be difficult to mount inside a boiler. I like it
because there is nothing to leek, unlike the previous device I had.

There is a wide choice of flow switches on ebay.

Worcester Bosch use a flow switch in their Heatslave oil boilers. The
switch is not very big. You might find one to look at an appropriate
supplier.


--
Michael Chare