Glow Worm Micron 120 No Switched Live (Boiler Help)

[John Player]

Hi All,

New to this so not sure if posting this questions is valid, but i have a boiler issue which has baffled me.

I have a Glow Worm Micron 120 boiler and it recently decided to die all of a sudden. I have had issues with the PCB in the past i.e i resoldered some dry joints a year ago. Thus i thought the PCB has broken, this time i opted for a new PCB but that changed nothing. I then checked the power comming into the boiler and it is getting 240v power, i then checked the Switched Live wire and it has no power at all, as a test i Jumped 240v from the main supply to the Switched Live supply and it all works, however only the HOT WATER in the house works and not the central heating, i then read a little and though that my thermostat which is a HORSTMANN 425 Tiara was the problem, i thought it was not sending the Switched Live signal to the boiler to turn it on, so i have replaced this with a new HORSTMANN 425 Tiara and still nothing, the boiler is not receiving the Switched Live to turn on, can someone point me in the right direction please?

I also have a Honeywell T40 Thermostat which has 240v at the connections and is wired correctly so i assume this has nothing to so with boiler not working?

Once again any help would be greatfully appreciated.

 

[ShaunCorbs]

Port valves ?

 

[John Player]

Port valves ?

Hi, thanks, is there any way to test these? I have a junction box where the switched live comes into from the thermostat and it has no power there also, im guessing it should at least have power there in the lines? Mains power is present in this junction box but just not the switched live which is wired with the vale wires.

Also there is no Switched Live in the HORSTMANN 425 also but it has full mains power?

 

[Ric2013]

deleted

 

[John Player]

deleted

Hi, i seemed to have no Switched Live in the HORSTMANN thermostat but there IS Switched Live in the Honeywell T40 thermostat, i did check all wires.

 

[ShaunCorbs]

You should have power on each leg eg heating on hot water on both should have power going to the port valves aslong as the stats are calling

 

[Murdoch]

Maybe time to get a pro in?

 

[John Player]

Maybe time to get a pro in?

If no1 is unable to help any further then i think your right

 

[Ric2013]

Only thing I can suggest is follow the circuit through logically and test your switched lives are 240V above a known neutral cable using a multimeter.

Check wiring diagrams for the individual components and never assume that the colour of the wire necessarily denotes what it has actually been used for!

A conventional system uses a 240V switched live from the programmer through the room thermostat and to the motorised valve. The motorised valve then opens and an internal microswitch switches a separate switched live to the boiler.

 

[fronty]

If you have a three way valve then you will only get heating if the motorised valve head has managed to open to valve into the heat position, it then closes a micro-switch which fires the boiler. Normally there is a lever on the head that you can push to manually operate the valve, I would try that first. It's possible the motor in the valve head has burnt out, or the microswitch has gone faulty, or the valve body itself is so stiff that the head can't turn it. The latter is the problem I had and I had to replace the actual valve body itself, it actually wasn't too hard a job. You can take the head off and use a pair of pliers to turn the spigot (it only turns about 1/8 turn, if that), it should turn quite easily, if it's stiff then the head might not be able to turn it and you'll probably have to replace the valve body.

 

[Ric2013]

If you have a three way valve then you will only get heating if the motorised valve head has managed to open to valve into the heat position, it then closes a micro-switch which fires the boiler. Normally there is a lever on the head that you can push to manually operate the valve, I would try that first. It's possible the motor in the valve head has burnt out, or the microswitch has gone faulty, or the valve body itself is so stiff that the head can't turn it. The latter is the problem I had and I had to replace the actual valve body itself, it actually wasn't too hard a job. You can take the head off and use a pair of pliers to turn the spigot (it only turns about 1/8 turn, if that), it should turn quite easily, if it's stiff then the head might not be able to turn it and you'll probably have to replace the valve body.

Good advice. Be warned, however, that manually operating the valve does not always actuate the microswitch, and it sounds as if the microswitch is working to some degree otherwise the boiler wouldn't fire at all.

To be honest, though, I'm thinking if the OP does not have the tools or inclination to test "is the valve or valves receiving the correct signal to power up" and "is the valve behaving as it should on receipt of said signal" using basic electrical testing (presence of live at appropriate terminals using wiring diagrams), then, while DIY is not going to be impossible, finding the fault may be enough of a mission that paying a professional could be a reasonable alternative to changing parts at random.

 

[fronty]

Good advice. Be warned, however, that manually operating the valve does not always actuate the microswitch, and it sounds as if the microswitch is working to some degree otherwise the boiler wouldn't fire at all.

To be honest, though, I'm thinking if the OP does not have the tools or inclination to test "is the valve or valves receiving the correct signal to power up" and "is the valve behaving as it should on receipt of said signal" using basic electrical testing (presence of live at appropriate terminals using wiring diagrams), then, while DIY is not going to be impossible, finding the fault may be enough of a mission that paying a professional could be a reasonable alternative to changing parts at random.

I didn't think the hot water used the microswitch, I can't remember how these things work but the hot water port is opened by default due to the spring return, and the programmer/cylinder stat controls when the boiler fires. Thought the microswitch was only used when the valve turned over to the heating position, can't remember what happens at mid position, there was a great video I watched a while back where some nerd described it all, I'll have to dig it out again as it was fascinating in a geeky kind of way. lol

It sounds like the OP is already down a few hundred quid, that Tiara is £60 in Screwfix and new PCB isn't going to be cheap, maybe time to get a pro in before more money is chucked at it (but check the valve turns easily anyway, that's free!). 🙂

 

[fronty]

 

[John Player]

Thanks all, i think i have a wire fault, as there is no signal (Switched Live) being given from the tiara at all, no signal at (switched live) at any of the valves or the main junction wiring box where the valves are wired into, hence i think the issue is within the wireing itself, if i bypass the switched live and give the boiler direct 240v jumped from its own supply it powers up fine.

 

[fronty]

Do you have power on the orange wire from the valve when the roomstat and programmer are calling for heat? If not, that'll be your problem.

 

[Ric2013]

My suspicion is the Tiara programmer hasn't been wired in correctly.

 

[John Player]

Hi All,

Thanks for everyone that has contributed, it was infact the honeywell motorized valves, both had failed, when i opened up the port body and manually moved the latch so that it presses against the micro switch, i then engaged all power and it all turns on, obviously its constantly on due to microswitches being pressed. Would you recommend changing just the upper body or the whole valve? Im tempted by the £25 ebay replacements albeit their not honeywell, has anyone used these? If so any good?

Thanks

 

[Ric2013]

How has manually pushing the valves open proved they won't open if they are powered up correctly? Seems to me what you've proven is that the microswitches work and that the permanent live to the valves works too, not that the valves are faulty. They may be faulty, but you haven't proven it (from what you've told us anyway).

You said the Tiara programmer was not giving a switched live output (post 14). If the valves aren't receiving a switched live or there is a neutral fault in the wiring then how do you expect them to open?

My advice is stop wasting money replacing parts you have not proven faulty and pay a heating engineer or a good plumber. Sounds harsh, but most people struggle with fault-finding logic and it's not an easy thing to learn. You're getting there, but then you seem to be skipping bits and going up dead ends.

If you want to learn and to play, buy yourself a cheap multimeter, download and try to understand the wiring diagrams for your compenents, and then you can test cables and trace faults to your heart's content, but be prepared to spend hours testing, so you do need to enjoy this kind of thing. Been there, done it, and I got good at it eventually, but it wasn't a fast process.

 

[fronty]

Hi All,

Thanks for everyone that has contributed, it was infact the honeywell motorized valves, both had failed, when i opened up the port body and manually moved the latch so that it presses against the micro switch, i then engaged all power and it all turns on, obviously its constantly on due to microswitches being pressed. Would you recommend changing just the upper body or the whole valve? Im tempted by the £25 ebay replacements albeit their not honeywell, has anyone used these? If so any good?

Thanks

Did you check that the valve opens when the motor in the head is energised? If the valve isn't opening then the microswitches won't get "pushed" and the boiler won't fire when heat is being called. As I mentioned earlier it might not be the head that's faulty, it could be the valve itself is too stiff for the motor to turn, try turning the spigot with a pair of pliers, it should require little effort to turn, I thought I mentioned all this already, am I going mad?