Boiler keeps running - No demand from controls

[Dorsey]

Hey guys, I've been trying to diagnose and fix a problem with a heating system and am pretty much out of ideas!

It's a standard Y-Plan,
Glowworm Flexicom 30sx condensing boiler (fitted in the summer)
Drayton room stat (RTS1 newly replaced)
Honeywell cylinder stat (L641A newly replaced)
Danfoss Programmer (FP715Si newly replaced)
Honeywell Mid Position Valve (V4073A - newly replaced (tried 2 different heads))

I've checked the wiring and redone it a hundred times and it is Per honeywell's sundial plan, and i've gone through everything I can think of to find what's keeping the boiler running.

Basically when the programmer turns the heating off i'm left with a residual 140V on the orange (switch live) which seems to keep the boiler live even though there is no demand. If I kill the power to the wiring centre and turn it back on this voltage disappears and boiler will stay off till timed on. But once it's been on it stays on...

According to the diagnosis steps on a thread I found which I think is taken from Honeywell's diagnostics tests...

"If orange has 50-150v, (when CH is switched off) there is a problem with the boiler "

When the boiler is still running d.08 is 0 -which I take to mean it knows there is no external demand for heat.

Is this likely to be a boiler fault then or is there something else I should be looking at? I'm nearly out of ideas so any help on where to look next would be muchly appreciated!

 

[fuzzy]

i think its the 3 port, it send a signal out on the orange when theres no hot water demand but there is a CH demand, if you getting voltage when no demand from either there must be some current leakage from the grey wire, is the grey showing 240v?

 

[Dorsey]

Grey does have 240v - but that's DHW Off so that's right to have a voltage on it isn't it? Orange does take 240v when it's meant to but it's this residual 140v (well, 138...) that seems to be screwing things. I'll take out the orange when it's playing up and see if its the wire or the terminal that has the voltage.

I was just going by this post: Y Plan Problem Solving - DIYnot.com - DIY and Home Improvement

which gave me a bunch of testing to do and then concluded that 50-150v on the orange with CH off was acceptable for the actuator and was therefore the boiler at fault.

And Honeywell do state that "a.c. voltage may appear on specified wire or terminals due to back feed from Three port mid position valve. "

I've tried 2 different heads on the valve and they both do the same thing - am I just doubly unlucky to have had 2 with this voltage problem!?

 

[fuzzy]

grey is hot water off yes but thats the only one which should be 'live' it seems the oragne is getting more voltage than it should, if there is no demand what would you expect to see on the orange wire? i dont know but i wouldnt think it would be 140vs???????? but your research says its ok so i must be wrong, let me know if you sort it

 

[m1439003]

Is your boiler situated outside? If so does your boiler have an internal frost thermostat that will activate itself once outside temp drops? This would explain why the boiler kicks once despite all heating and hot water being off inside the house?

 

[Dorsey]

No frost stat on this one unfortunately and it's in the utility room/kitchen. I did read a very similar post on the interweb and the frost stat was causing the problem for that guy so it would have been nice as his symptoms seemed really really similar. (FYI: Nightmare system wont turn off. - Central Heating & Air conditioning & Ventilation - DIY Forum - Diy Doctor )

Thanks for the suggestion tho :s

 

[Dorsey]

@fuzzy - I'm not saying you're wrong and I really wish you were right - it does seem high to me too! As I type this it should have gone off according to the programmer - but it's still fired up and heating with the 140v on the orange terminal.

I've just removed boiler switch live from the terminal and the boiler is STILL going. Does this point us towards an internal boiler somethingorother?

 

[JimH]

Dorsey - where exactually did you disconnect - terminal 10... wire from above or below? If you disconnected from below it would be impossible for that boiler to run?

 

[Dorsey]

Hey Jim...

It'd be terminal errm 8 according to the terminal numbers on the honeywell thing (its not a honeywell wiring centre but i've connected each wire to where it should be as if it were)

It's the terminal with Orange from Valve and 1 from Cylinder stat.

This just leaves the permanent live connected (same terminal as the spur that feeds the wiring centre and programmer)

 

[JimH]

Any way you can show me the circuit diagram you are using? Okay... looking at the "W"... terminal 8 it is.
Still the same... if you have disconnected the wire from the bottom, the boiler can't come on. When you try this, is the pump running or off?
You will have 140 v ripple on the orange - perhaps not quite so high - there will be a few spurious volts raising the v.

 

[Dorsey]

With this disconnected - it's as if i've left the wire in - the boiler is still running and with the burner lit supplying heat still.

 

[Dorsey]

I've checked the wires aren't transposed anywhere along the way to the boiler as the voltage appears on the switch live at both the wiring centre and the wiring cartridge under the boiler... so the correct wires are going where they're meant to - unless the integral connections to the boiler have been miswired in manufacture so that s/l and live are on the wrong pins? :S

 

[JimH]

As I said - I don't have the wiring diagram you're working to, so it makes it pretty hard going - switch off the central heating... remove both wires from the bottom of terminal 8 - put one in 9 the other in 10 (they should be empty?), then switch back on again - what happens?

 

[gasmarc]

i am not saying this is the fault but something worth checking is the switch live and the permanent wires in the boiler are not the wrong way around , this happended to me before and ended up to be a time consuming exercise

 

[JimH]

i am not saying this is the fault but something worth checking is the switch live and the permanent wires in the boiler are not the wrong way around , this happended to me before and ended up to be a time consuming exercise

Just heading towards checking the boiler & pump gasmarc... really could do with clear photo's of the wire connections onto both?

 

[gasmarc]

i maybe wrong but check the wires into the boiler I presume you will have a permanent live wire and a switch live , disconnect them and switch power back on with no demand and see which is the permanent live and which is the switch live ,if they are ok ,it would be a zone valve It cannot be anything else that I know of ,good luck

 

[Dorsey]

I think i'm there.... Taking out the switched live and it having no effect on the boiler was what got me onto this. (PS... the wiring diagram that i wired to was the one that comes with the honeywell MP valve)

The 5 core that feeds the boiler from the wiring centre had been cut back to look like 4 core - there was actually a second black wire that the original installer had cleverly used at one end and then the other black at the other! I wasnt sure how it was ever made to provide any heat at all until I noticed the 24v ebus link was left in. With this removed and the wiring as it was the boiler didn't fire so the installer had left it in. This caused d.25 to be 1 and kept it running.

With the correct ends of the 5 core revealed and the ebus link removed... magically it worked, and the voltage when there was no demand for heat onto terminal 8 (orange from valve and switch live...) fell down to around 30v.

That'll teach me to trust other people's work! Thanks for all the suggestions tho people and although i'm not sure this lesson will ever help any of you it's helped me understand heating systems and wiring a lot better!

Merry Christmas and thanks again

 

[gasmarc]

Nice one that will make your christmas, you never stop learning in this job thats for sure lol

 

[TonyMJ]

I had exactly the same problem with my Keston boiler. I solved it by putting a largish resistor in series (i.e signal to boiler went through resistor). Suspect that the residual current on the control wire must be just enough to trip the relay.

 

[Suzzane]

it seems to be tri port, orange receives signal from the port when there is no hot water demand ,grey wire seems to be leaked