Glow worm Micron 80ff LS trigger voltage?

[jamesmccosh]

My Micron 80FF is controlled by a Horstmann H27 programmer and a Honeywell 3 port valve.

The valve orange wire is connected to the LS on the boiler. When heat is required this carries the full 240 volts to indicate that the boiler should fire up. However, if the valve is fully towards A branch, central heating, and heat is not required this connection is still 216 volts as it is connected via the valve's internal resistors to live. As a result the boiler continues to fire although heat is not required. At one time, with the same wiring, the boiler would shut down but delay shutting down the pump just as it should.

Has the trigger voltage on the LS connection changed? What should it be? If LS needs to float (no voltage applied) to effect the proper shutdown, how did it ever work with this wiring? Is there a simple fix to prevent the boiler firing at 216 volts?

I've had various engineers servicing the boiler and changing the pcb and I can't afford to keep paying for them. I've changed the programmer and the valve to no avail, and studying manuals and measuring voltages has left me stumped.

I should be very grateful for any suggestions.

Regards

 

[twgas]

Disconnect the orange, and make it safe, then do you get mains power to the orange wire or the terminal you disconned it from?

 

[jamesmccosh]

Disconnect the orange, and make it safe, then do you get mains power to the orange wire or the terminal you disconned it from?

Hang on I'll go and try.

 

[jamesmccosh]

Disconnect the orange, and make it safe, then do you get mains power to the orange wire or the terminal you disconned it from?

In the state I described above, there's 230 volts on the orange and 39 volts on the terminal it was connected to.

 

[twgas]

Looks like the valve, do you have 230v to the white and/or grey?

 

[jamesmccosh]

Looks like the valve, do you have 230v to the white and/or grey?

0v to white, 240V to grey. The valve is brand new, fitted today.

 

[twgas]

0v to white, 240V to grey. The valve is brand new, fitted today.

these readings are right so I would say your new valve is faulty, was it a complete valve or just the powerhead?

 

[jamesmccosh]

[/quote]these readings are right so I would say your new valve is faulty, was it a complete valve or just the powerhead?[/quote]

I bought a complete valve but just replaced the head.

Referring to the diagram in
www.gasheating.co.uk/mid-position-valve.html
What value are the resistors R1 and R2? If little current is being drawn, wouldn't there be nearly mains on orange if SW1 is closed and mains on grey?

James

 

[jamesmccosh]

0v to white, 240V to grey. The valve is brand new, fitted today.

these readings are right so I would say your new valve is faulty, was it a complete valve or just the powerhead?

My problem was that the orange wire is near mains voltage when either white or grey is at mains and the valve is fully open. It turns out that in this state the orange wire is always connected either to the white or the grey, if not directly, then via 280K ohms. This means that, unless current is drawn, the orange wire will be near mains voltage if either the white or grey are at mains. Therefore LS on the boiler is near mains and the boiler continues to fire.

This led me to consider that the boiler was faulty in not drawing any current from LS. Then I got lucky! In a kitchen drawer was a very old pcb - don't ask me why I'd kept it. Also in its box was a capacitor and an addendum sheet explaining that it was necessary to attach the capacitor between LS and Neutral to stop the boiler form firing when no heat was called for. Some expensive engineer had not fitted or re-fitted the capacitor at the recent change of pcb.

Problem solved. I think I will dispense with engineers now.

 

[twgas]

Well done. Sorry I didn't give the capacitor a thought as I've always fitted them and never thought anyone wouldn't.

 

[jamesmccosh]

Thanks. However, in order to avoid the circuit tracing I eventually had to do, I replaced first the programmer and then the motorised valve - both unnecessary. Still, the approximately £100 outlay is cheaper than a visit from an engineer and I've now given the system a new lease of life and I have a couple of spare components!

James