Out of my depth (admittedly)

[moosey86]

Right guys heres the situ...

Went round a job for my mate whos said he'd changed a conventional boiler to a system boiler on a y plan system. Valiant the make. He wanted me to identify the two 3 core flex's previously wired into the old boiler. One being the supply, and the other i thought would be for the stat, which my mate (the plumber) said it would be.

So I checked it out and I got 0V from brown wire with stat open, and 230V with stat closed. Blue stayed the same all the time, I cant remember what it was but it was low. Green/yellow being earth. So the brown is obviously the switch from the stat. He said the switch then just had to be put into terminal 3 or 4 of the boiler (Valiant Ecotec if it helps) to let the boiler know it was calling for heat. This didn't work, and after a couple of hours of messing around I didnt sort it so I put the link back in 3 and 4 and I walked away (head down in shame and no money in my pocket). But I will add I haven't had any experience in central heating systems and its the weakest part of my game!

But whilst driving home I remembered that the 3 port valve wasn't operating when the stat was being operated. And I thought that maybe it was linked through the old boiler so if I linked the brown switch wire with the blue wire from the same flex that it might send a feed up to the 3 port valve to operate. I know I can bell out the cables at the junction box to prove my theory but I just wanted to see if any of you think that what I'm saying might be true! Im not ready to admit defeat as I say I dont have the most experience in this field but i'd like to go back tomoro night and see if i can sort it unless someone tells me that there is no way that this would work I will prefer not to make myself look like an arse again.

Cheers guys, ive got another question for u too once this is cleared up! That will be in the industrial section tho.

Thanks

 

[JonAW]

My advice is to be very careful with a boiler. I went to a job with a plumber friend to wire up a replacement boiler. The original boiler had ruptured but the old burner was still being kept so all I had to do was rewire in the burner. I thought I was going to just connect the wire from the stat into the burner but when i got there, there were 2 wires going into the burner, 1 from the power supply and 1 from the stat. So I wired the stat and power back up and didn't look at the burner controls. What we discovered after 15 min or so was that the stat had activated to stop the burner but the burner was not stopping. The only way to stop the burner was to turn off the timeclock. After an hours fidlling around with the burner wiring and testing the stat, I was able to take the supply from the timeclock directly through the stat and then down to the burner, as I had orignally expected to have to do.

This was probably the reason for the boiler rupturing as it would have kept heating until the timeclock was turned off or the internal stat was activated. The radiators in the house would also have been dangerously hot as well.

I was just looking at the wiring off the boiler again and although the manufacturers suggestion is fine I would prefer to break the power to the boiler through the timeclock, valve, roomstat and boiler stat instead of breaking the start signal through these components as it may be possible for that run signal to fail and the boiler would still have power whereas breaking the power to the boiler through the external components would prevent it from running if terminals 3 and 4 were faulty. I am also assuming there is a water temperature stat internally on the boiler as there should be a stat to cut it out in overtemperature.

regards

Jonny