CH boiler died - please help if you can

[Alex]

Hello

A bit unfortunate this to happen on 1st Jan! :(

We have an old Vailant VCW-SINE-18T3WFH with Danfoss 103 timer and a Honeywell thermostat.

The Thermostat (still on as far as I could tell) was found with the blue wire dangling as it fell from the wall (the screw must have been lose). While moving the thermostat (stupid me not to turn the unit off first) the wire made contact with (I think) connector number 4 inside the honeywell thermostat. A spark followed and the unit turned off. :(

The fuse on the mains and for the heater seems fine (I can hear the timer ticking), but the unit remains off - the main light at the bottom remains off even after turing it on.

I would need the wiring diagram of the Honeywell thermostat - does anyone have one? It has 5 wires coming in. Right now number 1 is connected to the brown wire, and number 3 to the green/yellow earth wire. Is blue supposed to go into 2, 4, or 5? Or could it be that the thermostat could have been permanently damaged?

Any suggestion obviously welcome, even not directly related to the wiring of the thermostat. Thanks.

Best

[Alex]

Following this, upon inspection, 2 and 3 (earth) are in parallel via a resistor. TIA,

[Set Square]

Your stat has 5 places to connect wires, you say. How many *actual* wires are there?

My guess is that there are 3 - or 4 at the most. If it's like the Danfoss stat which I have, the connections are as follows - by *function* not

*colour*!

The live CH ON feed from the programmer goes to 1. The switched live to the boiler goes to 2. Neutral goes to 4. [The resistor which you mention provides a small amount of heat when the boiler is running, and makes the stat a bit more responsive - and is likely to be connected between 2 and 4 rather than 2 and 3. Note that the terminals may not be numbered sequentially, for good measure!]. Assuming the stat has change-over contacts, 3 is the connection which you would use if you were controlling a cooler rather than a heater, and is not used in your case.

You will have to work out which colour wire provides which function by looking at the connections at the other end of the cable. All too often the green/yellow wire (which should mean earth!) is actually used as the switched live. Dangerous practice!! Chances are that the stat says "This device must be earthed" but that there isn't actually an earth wire going to it!

[Alex]

Many thanks Set - really appreciated. It is now too late to work out the meaning of the wires by looking at the timer and can only report their colour unfortunately.

But I have looked at the stat closely. It is as follows:

1 4 3 2 5

Brown Empty Green/Yellow Empty Empty | | | | | | | | \ / | \ / | \ / | \ / | \ / | Resistor \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / C

Notes: C=blue round thingy (capacitor?). The blue wire (do not know the function) is currently *not* connected.

Note numbering is the numbering on the box. 5 actually has no electrical connector just a numbered place in the box.

I have tried shortening the circuit by connecting the blue cable to 1 together with brown hoping it would generate an on signal to no avail.

What puzzles me most is that the light on the switch of the boiler remains off even if I switch it on. OK it may be that the bulb is blown but I am suspicious actually no electricity is reaching the boiler. On the other hand the fuse outside is fine (is there an internal fuse as well?) and I can hear the timer ticking...

Thanks

Alex

[larry]

Check the fuse as the timer may have its own battery to keep it going in the event of power failure.

larry

[Lee]

There are some wiring diagrams on the Honeywell UK site. See if you can find the model number off the stat and look here:

timer is just a straight on/off I think. Possibly if something has been shorted, there is a blown fuse or burnt track somewhere?

Lee

[Set Square]

You've pretty certainly blown a fuse somewhere - make sure you've checked

*all* possible locations.

Connecting the brown and blue together is pretty likely to blow a fuse if it wasn't already blown! Unless I'm very much mistaken, blue is neutral and needs to be connected to 4. I still suspect that green/yellow is (incorrectly!) being used for switched live. I would expect this to be connected to 2 - but 3 *may* be right depending on the exact design of the stat.

So connect blue to 4 and then find and fix your fuse, and have another go!

[Andrew Sinclair]

In message , Set Square managed to combine nouns and verbs in a pleasing form to communicate the following;

I'd concur, our (Worcester) boiler has a fuse on the main circuit board in addition to a regular fuse on the incoming supply.

You might need to do a bit of dismantling to get to see where the fuse is so make sure the power to the boiler is off before you start poking around.

Andy

[Alex]

Dear All

Many thanks to Larry, Lee, and Set Square again. Very very useful. Here's what I found:

1) the thermostat. It turns out to be a frost stat(!) T4360: least this is exactly the same to what I have, including the internal wiring diagram - the others are different). So it looks as if my blue wire goes into 2.

Important: My understanding is that this is a on/off circuit, the stat simply closing the circuit whenever the outside temperature is below what requested thereby signalling the boiler to kick in. So even by shorting it, should I not simply be bypassing it? Not that I am going to try, but I'd like to know. Anyone?

2) Struggling to find any fuses to check (the one before the timer is fine) I opened up the boiler. It has 2 fuses of 2 Amps each inside - I do not have any of these in the house - I'll try replacing them tomorrow.

So situation is: 2 fuses in the boiler may be blown - to be tentatively replaced tomorrow, and the blue wire seemed to go into 2.

Any further comments/advice much appreciated. Else I'll try tomorrow as above and report back to you.

Many thanks again!!!

Best

Alex

Alex wrote:

[Set Square]

(At least this is exactly the same to what I have, including the

If it is *truly* a frost stat, it is an additional device to bring the heating on in case of frost when it is not being turned on by any other means. In other words, it by-passes programmers and romms stats etc. In this case, the heating should still work by 'normal' means even if this is disconnected.

HOWEVER, despite it being described as a frost stat, I suspect that it is being used as an ordinary room stat - since it has a working range of 3-20 degC. What is it actually set at? [20 is a bit low as a max temp for a room stat, but you *could* use it thus].

Anyway, whatever its use, the wiring will be 1 (live) brown: 2 (neutral) blue and 3 (switched live) green/yellow (God help us!).

Do you have any means of testing the continuity of your fuses? If not, you ought to get some test equipment if you're serious about DIY!

[Lee]

I think you need to be sure what the "earth wire" is connected to, and which wire is the actual "heating load" wire. Don't go by the colours alone. I'd guess, as someone else mentioned, that the "earth" wire is being improperly used as either a "neutral" or "heating load" wire.

Quite obviously, if the live and actual neutral are connected together it won't be good... :)

Lee

[Alex]

My understanding is that the basic wiring and casing is the one of the reported above for the frost stat, but at some point Honeywell produced one in which the termo switch inside goes higher than 20. In fact on my wheel it goes up to 30. All the rest is identical, including all the wiring.

I've now reinstalled the blue wire into 2. Brown and yellow/green were never removed so are still there as described. I agree - looking at the wiring the use of green/yellow is wrong.

I looked so hard for the fuses that upon finding them in the boiler I was sure it was those. While removing them it was so dark I snapped one. I tested the other and I found it working OK. I'll go and buy some tomorrow and try with them. I hope it's the fuses as otherwise I am left with no ideas on how to bring the thing back to life!

Once again, many thanks for all your help. Will post an update tomorrow...

Alex

[Alex]

Further to all this.

Finally managed to find some 1Amp fuses at B&Q to replace the ones hidden away in the boiler. Replaced them and the boiler fired up OK. So blue wire did indeed have to go into 2 as per wiring on the web site below.

Many thanks to all of you for your help.

Off for a hot shower now!

Cheers

Alex

Alex wrote:

[raden]

In message , larry writes

You are joking, aren't you

Of course, a wire or microswitch contacts might have melted

[raden]

In message , Andrew Sinclair writes

The Sine 18 control pcb has a 80mA (I think) fuse on the board, but I doubt that it would have blown, more likely one of the (two) 2A fuse on the switch pcb

It's possible that a short could weld the contacts in one of the switches on the switch pcb, or blown a track.

[raden]

In message , Alex writes

They should be 2A if they are in a black plastic housing on the switch pcb