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?

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'm wondering if all the failures have been down to inductive loads.
Perhaps a VDR or R/C suppression (or both) should be considered before
choosing your next micro-switch or similar?

A branded microswitch should be very reliable, if treated well.

On Wed, 22 Nov 2017 12:55:35 -0800 (PST), Cynic
coalesced the vapors of human experience into
a viable and meaningful comprehension...

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?


It sounds like the back-EMF of the relay coil has a tendency to weld
the reed contacts together. I would *expect* that to happen! which is
odd given that it's a manufacturers modification.

What is the voltage across the relay's coil when it is energised?

If I am right about the cause, a silicon diode wired across the coil
with the cathode (marked terminal) connected to the positive side (ie
the diode is reverse biased) will snub the reverse EMF.

Check there isn't a diode in that position already.
--

Graham.
%Profound_observation%

On 22/11/2017 21:57, Graham. wrote:
On Wed, 22 Nov 2017 12:55:35 -0800 (PST), Cynic
coalesced the vapors of human experience into
a viable and meaningful comprehension...

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?


It sounds like the back-EMF of the relay coil has a tendency to weld
the reed contacts together. I would *expect* that to happen! which is
odd given that it's a manufacturers modification.

What is the voltage across the relay's coil when it is energised?

If I am right about the cause, a silicon diode wired across the coil
with the cathode (marked terminal) connected to the positive side (ie
the diode is reverse biased) will snub the reverse EMF.

Check there isn't a diode in that position already.

Unless Cynic comes back with different information, I would expect the
relay solenoid supply would be AC. If so, you wouldn't want a diode
across the winding.

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

Fredxxx wrote:

On 22/11/2017 21:57, Graham. wrote:
On Wed, 22 Nov 2017 12:55:35 -0800 (PST), Cynic
coalesced the vapors of human experience into
a viable and meaningful comprehension...

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?


It sounds like the back-EMF of the relay coil has a tendency to weld
the reed contacts together. I would *expect* that to happen! which is
odd given that it's a manufacturers modification.

What is the voltage across the relay's coil when it is energised?

If I am right about the cause, a silicon diode wired across the coil
with the cathode (marked terminal) connected to the positive side (ie
the diode is reverse biased) will snub the reverse EMF.

Check there isn't a diode in that position already.

Unless Cynic comes back with different information, I would expect the
relay solenoid supply would be AC. If so, you wouldn't want a diode
across the winding.
Indeed in my similar vintage (2003) Firebird the relay was fitted from
manufacture and was a standard 'octal' 11 pin type with a mains coil.
My flow switch only failed once, and that was also water leaking through
the paddle seal and through the electrics to the outside world. I am
unconvinced that a much better one can be easily found, but I am biassed
because it was probably the only part of the boiler that only failed
once.[1]

[1] Apart from the terminal rusting through of the main thermal store
which is integral with the boiler heat exchanger.

--

Roger Hayter

Michael Chare wrote:

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...h-brass-ac-10b
ar/dp/1006768?CMP=i-bf9f-00001000

but it might well be difficult to mount inside a boiler. I like it ecause
bthere 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.
As long as you run another cold feed to the filling loop the supply to
the hot water heat exchanger can come from outside the boiler via the
flow switch and a flying lead from the external flow switch can be
connected into the control box (which is the existing arrangement, but a
shorter lead).

--

Roger Hayter

On 22/11/2017 23:04, Roger Hayter wrote:

I use one of these:

http://uk.farnell.com/gentech-intern...h-brass-ac-10b
ar/dp/1006768?CMP=i-bf9f-00001000


I paid £24.43 for that flow switch in Feb 2011. They are now more than
3 times that!

--
Michael Chare

I'd have thought using a relay as they now do would stop issues of arcing in
the switch which can become conductive. have you actually proof its become
wet?

Might be worth looking into it further by looking at the wiring and what
current the relay is taking and also trying to stop any kind of arcing with
a snubber network. A few days even for this sounds wrong to me.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Fredxxx" wrote in message
news
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'm wondering if all the failures have been down to inductive loads.
Perhaps a VDR or R/C suppression (or both) should be considered before
choosing your next micro-switch or similar?

A branded microswitch should be very reliable, if treated well.

Actually looking at the switch innards is virtually impossible without cutting the plastic assembly to pieces.
I could understand the contacts of the reed welding but surely the result would be a closed circuit regardless of the position of the actuator paddle magnet. Moving the paddle gives closed circuit or resistive path instead of closed/open which is what it started with when first installed.
I'll probably end up taking the switch back as defective but what's to say another won't be as crap.

That's correct. It's a 240 volt ac circuit.

Seems ideal but a lot of money for the unit. I could quite easily modify the mcws pipe to allow a vertical upwards mount.