CH Not working, HW Fine.

[jm555]

First of all I will say hi and thanks for any help or advice. I seem to have a common problem. I am no CH expert but I am a qualified aircraft engineer, so I can work things out fairly well. If not, I will pass this on to someone more qualified.
My CH will not come on. The timer is a Danfoss fp715 and the light is on. If I turn up the thermostat, a Danfoss RMT230, it clicks but the boiler will not light. My system is a Vokera Mynute 20e combi boiler with a hot water tank.
I removed the cover from the thermostat and I was presented with 3 wires connected to it. Red, Blue and yellow. Assuming blue is neutral, I get 240v from red and nothing from the yellow. When I turn the dial down past 18 degrees I get 240v from the yellow.
I assuming the thermostat is faulty but I am having no luck in finding a suitable fault finding guide.
Any help will be appreciated.
Jamie

 

[Hellmendyeh]

As far as I'm aware the vokera mynute is a system boiler so should have 2 2 port motorised valves or 1 3 port, most likely there is where your problem lies. Should have a manual lever to move into on position that will let you know if it is the fault, located normally at Boiler or close to cylinder

 

[Armo74]

Synchron motor failure in the motorised valve.

 

[jm555]

Thanks for the quick replies. Would it be possible to see a picture of the valves so I can work out which one I've got?

 

[Armo74]

Hopefully someone will be along to upload a picture,in the mean time you should be looking for a valve with a plastic or metal silver box on the side of it.
The valve will have 2 or 3 22mm pipes coming from it they are usually near the pump and cylinder.

 

[jm555]

I hope this helps!

 

[jm555]

 

[Whitespirit66]

Untitled

• Whitespirit66
• 4 Feb 2013
• 4

The above is a 2 port. Alternatively, you may have a 3 port, with an extra connection for a third pipe in the middle.

 

[jm555]

I've had a look but no joy. I can't see anything like that near the boiler or the hot water tank. I wonder where they would hide it? Which water line should it be on?

 

[jm555]

The more I research this, the more it makes sense. My house is a 3 storey townhouse. The boiler is in the garage, the hot water tank is on the top floor. Would the loft be a suitable place to locate the pump and the motorised valve? I'll have a hunt in the morning, meanwhile I'll dig out an extra duvet!!

 

[jm555]

Right, found them. 2 2 port motors. Switched them both to manual and now the heating works.
Now, which one is faulty!

 

[Blagard]

Take them off manual and put the HW only on.

Check the manual levers and you should find one that is floppy/loose or has moved over. That will be the HW one.

Now turn HW off and put CH on and check the Valves again. The HW one should now have returned and the other one should be floppy/loose or moved over, if not it is not operating.

Now to find out why!

If you trace the cable to the CH valve back to the wiring centre you need to check if the brown is live. If it is, your Actuator head needs replacing as the motor is not driving the valve open.

If the brown is not live then it may be your room thermostat is not calling for heat or is broken.

Info on the valve below:
http://danfoss.ipapercms.dk/Heating/AutoGen/29267_32200/?ForceLanguage=en-UK

 

[jm555]

Qualified aircraft engineer and cant work out putting a clock to HW or Ch and seeing what valve moves and which doesnt.
Get your qualifiication in a lucky bag ?

Cheeky!!!
Right, I've sussed it. It's the lower one of the 2. They are both getting a 240v supply when they should. HW goes floppy when switched on. CH isn't doing anything and has spring resistance the whole time.
Thanks for the help.

 

[jm555]

Perhaps I was a bit quick in updating this thread before I worked out what was what. It may be basic, but without the knowledge or experience, proceed with caution is always my mantra.
There is nothing especially complicated about my job either but if I were to drop you straight in to diagnose a basic fault, how confident would you be?
On the other hand, If I gave you some rudimentary training on the system in question, I'm pretty sure you could probably come up with a sensible solution providing the correct questions were asked.

 

[gas112]

Easy , aircraft engineering its not rocket science is it