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

 

[Spudnik]

Looking at page 28 it looks like you should have 3c & e to the stat.

http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/839592_09.pdf

 

[moosey86]

that is correct there is a 3 core and earth to the stat, in twin and earth from the connection unit in the airing cupboard...

 

[Spudnik]

And have you connected it as in the diagram pictured?

 

[moosey86]

no i haven't changed anything. The wiring has been left the same as what it was, a y plan with a conventional boiler. But if the un-identified flex at the boiler goes up to the connection box upstaires I could soon sort it. I take it thats what you're getting at?

 

[Spudnik]

Have you checked the wiring diagram in the link^^^^ i posted?

If not, have a look and maybe print it off and take it with you.

See how that goes

 

[moosey86]

Thanks jason, I know it can be hard to explain something like a central heating system to someone without being there and looking at it yourself. I'l take the diagram but i dont see how it would tell the 3 port valve to open if a cable went from the boilerto the stat. If i dare go back il let u know how i get on. Thanks alot.

 

[Yooj]

I don't think that you would need the motorized valve (3 port valve) as the new boiler is a combi, and therefore does not require a hot water tank, as all hot water is delivered on-demand. The control of how-water or heating is done internal to the boiler I think...I would suggest you talk to the boiler installer on this bit though to confirm.

The simplest test for this boiler as far as I can see is to leave the stat link in and make sure that there is a permanent electrical supply...this should allow the boiler to fire up when there is a demand for hot water (not heating though). In order to get the heating going, the time-switch controller needs to be provide a demand signal to the boiler.

As far as I can see, the other flex you are talking about is probably the feed for the 3-way valve, and the water pumps which are probably in the airing cupboard.

It is difficult to visualise without actually seeing it, however maybe you could do a continuity check or something on this other cable and see if it doe infact go to the airing cupboard. (I bet it does), in which case you probably do not need it.

Yooj

------------------------------------------------------------------------------------
Ah...just read that it is a system boiler and not a combi...my bad .

Will read more, and post further thoughts.

Always 'draw, aim, fire'...and not 'aim, fire, draw'.

Yooj

 

[Yooj]

Right...I have had a chance to think about this....Vaillant manuals are useless, in that for the system boiler fit, they just canibalise the combi manual but don't give too much info.

Anyhow...a couple of questions:

1. With the link in situ between 3 & 4, does the boiler fire up? If not, then there is another issue, probably to do with the boiler installation. If so, then it is definately controls related.

2. Why did the person fitting the boiler not install the controls as well?

Other than that, for a set-up with a motorized valve, the wiring will look something like the attached picture, though probably not exact, but it will give you something at least to go on.

Take a look in the heating controls junction box...probably situated in the airing cupboard. Likely to be a 2 gang blanking plate covering it. Familiarise yourself with the wiring, see where it goes and understand the likely layout and function. Do this before connecting up anything else, as you do not want to inadvertently blow up a board in the boiler.

Yooj

 

[moosey86]

The boiler does fire up with the link in 3 and 4. Im going back round tomorow at some point so i will have a proper look at the system and get to the bottom of it. I'l let you know how i get on hopefully it will be sorted otherwise i will be asking u some more questions.

Cheers Yooj

 

[Yooj]

Did you get to the bottom of this?

Yooj

 

[moosey86]

i had to do another job today, i didnt get sorted till 3 so i was in no 'sit down and take your time' frame of mind. Its a night off the booze, a date with call of duty, a drunk girlfriend strolling in later and then central heating in the morning

 

[Yooj]

Come on, admit that you really have been watching X-Factor and not playing COD

Yooj

 

[moosey86]

sky+ is a god send. im watchin it now, should be finished in time for MOTD and then its ****ed bird time..... sweet

 

[moosey86]

Just to let you know yooj, i went round there last night and sorted it out. I took the take it all apart, find out what everything is, and put it back together approach and it worked first time. I'd do that pretty much everytime now, it only took a couple of hours!

I couldn't understand why it didnt work in the first place tho, i thought the boiler needed to be fed permanently but the diagrams showed to wire the boiler to the orange wire of the motorised valve which is also connected to the call side of the cylinder stat.

I thought the orange must of been common but then i thought it cant be because its calling on the the cylinder stat.

Anyways I turned it all on and the boiler only came on when the hot water was on on the programmer. I didn't think that was right but you generaly dont turn your hot water off so as it was getting late I thought if it all works i'l keep my mouth shut and sort it out later if it is wrong. The rads and thermo worked and there was hot water coming from the taps so I was happy.

Does this sound right? I'd like to know!

programmer - http://www.horstmann.co.uk/downloads/ElectronicDocuments/Central-Heating/C21-InstallerGuide.pdf

boiler - http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/ecoTEC_installation_and_servicing.pdf

and it was a y plan system, just the room stat, cylinder stat, 3 port valve were needed plus boiler and programmer. No frost stat

 

[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