Old Firebird 90 thermostat issue?

[Avo Mk8]

Apologies for my ignorance, I'm not clear on the 3 port reference?

A 3 port valve switches boiler flow between hot water cylinder and radiators, a common method called "Y plan", and is the scheme in the circuit diagram you posted with the thermostat etc. The valve looks like the pic below, and is probably near your hot water cylinder, but might be elsewhere. The boiler flow output goes into the bottom port, the rads come off one side and the cylinder the other.
Or the other option is you have two "2 port" motorised valves, one for hot water and one for the radiator circuit (called 'S Plan').
I'm keen to know if a 3 port is actually what you have, because it's the orange wire out of this valve that is providing the power for your boiler! And these things are known to get stuck etc!

Just to say that's it's clear now that the reason you boiler is running all the time is nothing to do with the boiler itself, it's that the power to it coming out of that junction box is not switching off when it should, so I think there's something up indoors that is causing your issue.

 

[unhandymann]

A 3 port valve switches boiler flow between hot water cylinder and radiators, a common method called "Y plan", and is the scheme in the circuit diagram you posted with the thermostat etc. The valve looks like the pic below, and is probably near your hot water cylinder, but might be elsewhere. The boiler flow output goes into the bottom port, the rads come off one side and the cylinder the other.
Or the other option is you have two "2 port" motorised valves, one for hot water and one for the radiator circuit (called 'S Plan').
I'm keen to know if a 3 port is actually what you have, because it's the orange wire out of this valve that is providing the power for your boiler! And these things are known to get stuck etc!

Just to say that's it's clear now that the reason you boiler is running all the time is nothing to do with the boiler itself, it's that the power to it coming out of that junction box is not switching off when it should, so I think there's something up indoors that is causing your issue.

View attachment 113539

Right thanks I understand, Yes I have to motorised valves ( Danfoss 087N6579 ) one for hot water and the other for the radiators so 2 port?

I changed actually one of these as it wasn't opening when I serviced it but when the inside control is switched to ' on' these both power up and turn as they should.and inlet and outlet pipes get hot.

 

[Avo Mk8]

Right thanks I understand, Yes I have to motorised valves ( Danfoss 087N6579 ) one for hot water and the other for the radiators so 2 port?

Thanks. The power for your boiler (and pump?) should be coming from the two orange wires of those Danfoss valves.
Circuit below (the 'junction box' you have may not have correspondingly numbered terminals, but the principle is the same!)
There are a number of tests you can do to see whether (being careful to switch off power while working) for example:

• If disconnecting both Danfoss valve orange wires stops the boiler working (which it should)
• If the voltage on the orange wires stays there when heating/hot water is satisfied/ timer is off (which it should not)

If one of those Danfoss valves is permanently on/open (or latched open) for some reason, your boiler will be permanently on.
Does this help at all do you think ?

 

[unhandymann]

Thanks. The power for your boiler (and pump?) should be coming from the two orange wires of those Danfoss valves.
Circuit below (the 'junction box' you have may not have correspondingly numbered terminals, but the principle is the same!)
There are a number of tests you can do to see whether (being careful to switch off power while working) for example:

• If disconnecting both Danfoss valve orange wires stops the boiler working (which it should)
• If the voltage on the orange wires stays there when heating/hot water is satisfied/ timer is off (which it should not)

If one of those Danfoss valves is permanently on/open (or latched open) for some reason, your boiler will be permanently on.
Does this help at all do you think ?
View attachment 113551

Thank you yes I understand the diagram and will try this tomorrow evening and report back the results thank you

 

[unhandymann]

So I haven't had the time or weather to get out the back and pull apart the wiring.

But I did turn on the timer inside and unpluged each valve individually and tried to shut them off via the controller but with with connected it continues to run.

Either one can be disconnected and the burner will continue to burn but with both disconnected it will not fire with the mains switch on, not sure if that helps narrow down anything at this point?

 

[Avo Mk8]

Did you conduct that experiment with both HW and CH calling for heat, or one of them, or neither?
It suggests to me that possibly at least one of those two valves is stuck, or one of the microswitches therein is welded closed.
I guess the next experiment is to find out which one is the problem. If you ensure neither HW or CH is on, and then repeat the disconnecting experiment, do you get the same result? You might hopefully find one valve disconnected turns the boiler off, but the other doesn't. It would be the one that doesn't that's the problem (or something in that circuit?)

 

[unhandymann]

Did you conduct that experiment with both HW and CH calling for heat, or one of them, or neither?
It suggests to me that possibly at least one of those two valves is stuck, or one of the microswitches therein is welded closed.
I guess the next experiment is to find out which one is the problem. If you ensure neither HW or CH is on, and then repeat the disconnecting experiment, do you get the same result? You might hopefully find one valve disconnected turns the boiler off, but the other doesn't. It would be the one that doesn't that's the problem (or something in that circuit?)

Both HW/CH on at the same time on the timer, unplugged each unit separately, then together and it will cut out.

One switch is brand new, so would assume it may be the other, they are turning the valve as they are ment to when powered on/off.

Yes I'll try switching on the controller tonight and do the same test on each valve, thank you hopefully getting closer to resolving this annoying issue.

 

[Avo Mk8]

Both HW/CH on at the same time on the timer, unplugged each unit separately, then together and it will cut out.

That seems to confirm to me that the boiler power is indeed coming via the valves, which it should.

One switch is brand new, so would assume it may be the other, they are turning the valve as they are ment to when powered on/off.

That's good the valves are doing something. The valve turning doesn't necessarily guarantee that the end travel microswitch gets operated. Or maybe the microswitch is just permanently on!

Yes I'll try switching on the controller tonight and do the same test on each valve, thank you hopefully getting closer to resolving this annoying issue.

To me the test is to turn off both CH and HW on the programmer, at which point you have said the boiler/burner still runs.
Then disconnect say the newer motorised valve.
If the boiler then cuts out, it's the new motorised valve that at fault, or it's not wired correctly!
If the boiler carries on running, it must be the older motorised valve that's faulty!

 

[unhandymann]

Hi Avomk8

Ok so test diagnosis still not sure.....


So mains switch on +

both valves disconnected
* doesn't fire (nothing works, timer has power and clicks between on/of red light comes on, with mains off the red light doesn't come on nor the switch/relay sound )

New valve disconnected & other original valve connected
* fires and runs valve operates (controller does nothing still)

New valve connected & other original valve connected
* fires and runs valve operates (controller does nothing still)

I removed the timer from the wall while both were plugged in and burner running and it shut down, so maybe a timer issue as both valves seem to be the same result?

 

[Avo Mk8]

OK clearly my suspicion of a valve being responsible is incorrect.
So that moves the problem back to the timer not doing it's job, or the wiring having an error.
I'm puzzled as to why there is a wire in terminal 2 of the timer. That is normally used when you have a 3-port mid position valve, eg "Y Plan"
Could you remind me what motorised valves you have, are they both 2 port, ie pipe in and pipe out. There's not a third pipe entering at the bottom of either?

It seems the timer itself is responsible for the 'always on' effect, but you say the indicator lights go on and off, and the relays click? Very odd.
Could you just confirm both the red indicator lights can be made to go on and off by adjusting the timer, and there is a 'click' associated with both?