How would you do this (boiler timeclock rewire)

[ProDave]

Todays problem from my letting agent:

Rented house, gas central heating.

Letting agent calls, says boiler has just been serviced, and the gas man says an electrician is needed to fix the timeswitch.

So I go and look. the time switch is not even connected.

It looks a fairly recent (but not brand new) Worcester combi boiler, so I'm guessing the timeswitch has not been connected since the boiler was changed, whenever that was, because the old wiring was incompatible.

The way it was wired was a 3 core and earth from the boiler (in the garage) to the timeswitch (in the utility room). Wired as live and neutral to the timeswitch, and switched live back to the boiler.

But the new boiler doesn't want switched live, it wants a volt free contact to switch a 24V circuit inside the boiler.

So my problem, how to re connect the timeswitch (which can be configured as a volt free contact) using just the existing 3 core and earth between the boiler and timeswitch. It's a major job to run another cable along this route.

My 2 "solutions" with their problems are:

Solution 1: the nasty dirty solution. Use 2 cores of the 3c&e for the L and N feed to the timeclock, and the third core plus the CPC as the low voltage switch contacts.

I don't like that as I don't like using a CPC for anything other than it's intended function, but there is in fact no need for a CPC at the timeswitch, and it would only be for a low voltage circuit.

Solution 2: Use just 2 cores of the 3 core and earth for the low voltage switch contacts. Then source a completely new L and N supply for the time switch from a FCU from a nearby ring main in the utility room.

Much better technically, but has the problem that the timeswitch is fed from a different supply to the boiler. Shouldn't be an issue but should I put a warning 2 feeds label on the timeswitch?

Anyone got any other suggestions?

 

[NozSpark]

Is it a Greenstar boiler?

 

[ProDave]

Is it a Greenstar boiler?

I don't know. I didn't think to note the model number as I don't see the significance. The only important thing is the heating control needs to be by a volt free pair of contacts.

 

[Doc Hudson]

Anywhere a contactor could be mounted near to the boiler to switch your low volt contacts. I don't like the idea of 230v & 24v switching in same cable, especially a bare cpc conductor. A faulty break of the insulation on the 230v live could put 230v down to your LV contacts.

Doc H.

 

[NozSpark]

One of these or is an older model completley?

 

[ProDave]

Anywhere a contactor could be mounted near to the boiler to switch your low volt contacts. I don't like the idea of 230v & 24v switching in same cable, especially a bare cpc conductor. A faulty break of the insulation on the 230v live could put 230v down to your LV contacts.Doc H.

I like that. Why didn't I think of it? headbang

It needn't be a high power contactor, just a relay with a 240V ac coil, in a suitable box screwed to the wall next to the boiler.

The timeswitch would continue to be wired as live, neutral and switched live energising the relay, and the relay would provide the volt free contact for the boiler.

Sorted. Thanks.

 

[Doc Hudson]

Sounds the best to me, and shouldn't be too expensive to implement.

Doc H.

 

[ProDave]

One of these or is an older model completley?

No nothing like that.

The case is all nice and square, none of the modern rounded stuff. Most of the case is white painted metal, except for the panel at the bottom with the controls which is grey plastic.

 

[batty]

could you not put timeswitch next to boiler?

 

[NozSpark]

Right,,, it the old 24i type then.. With a temp selector, timeclock and pressure gauge on the front L-R

It's not too difficult to wire a timeclock in, but you'll have to do it to the terminals underneath.

Take your perm live and neutral from the supply terminals and take the switched live output to the LS terminal,,, this will then go through the stat and back to the LR terminal to fire the boiler and start the pump.

HTH

 

[ProDave]

could you not put timeswitch next to boiler?

The timeswitch is in a convenient place in the house in the utility room. The boiler is in the garage, so not as convenient for access. Best leave it where it is, now Doc Hudson has shown us the easy way to rewire it leaving it where it is, and using the existing wiring.

---------- Post Auto-Merged at 21:20 ---------- Previous post was made at 20:52 ----------

Right,,, it the old 24i type then.. With a temp selector, timeclock and pressure gauge on the front L-RIt's not too difficult to wire a timeclock in, but you'll have to do it to the terminals underneath.

Take your perm live and neutral from the supply terminals and take the switched live output to the LS terminal,,, this will then go through the stat and back to the LR terminal to fire the boiler and start the pump.

HTH

I should have spent more time making more notes.

From L to R there's a power on indicator, a heating on indicator (and switch) and a hot water demand indicator, then a pressure guage. That may not be 100% but it's something like that.

The live feed terminals were just two terminals, with one of those horrible "washer under a screw" earth terminals. Next to the mains in terminal block was a terminal block with 4 terminals. The middle 2 were bridged with a wire jumper. Removing the wire jumper turned off the heating, and with the jumper removed I measured 24V across them.

While you might well be right, I didn't see any way to provide a switched live to activate the heating, just this contact switching some internal 24V circuit.

Note to self. Before asking a question on the forum, write down the exact boiler model number first.

 

[NozSpark]

The jumper wire takes the place of a room stat,,, one of the terminals is labeled LS (live switched) and LR (live return)

LS is only live when the time clock says so and LR is only live when the time clock and roomstat say so IYKWIM?

LS and LR are 230v contacts,,, not volt free!

The built in time clock termnals might be volt free though!

 

[ProDave]

The built in time clock termnals might be volt free though!

Perhaps I didn't make myself clear. There is no built in timeclock with this boiler. There's just a switch to manually turn the heating on and off. The switch is in a round panel in the bezel, so perhaps there was a (not fitted) option to have a time clock there?

I don't know how long it's been like this, but the tenants have been going into the garage to switch this switch to turn the heating on or off manually whenever they wanted it on. Hence why I'm reinstating the timeswitch in the utility room that was previously disconnected by persons unknown at a time unknown.

 

[NozSpark]

Here's a link to the worcester bosch discontinued range literature

Discontinued gas boiler literature - Worcester, Bosch Group UK homeowner site

I recon you've got an i series boiler, they were very popular before the new ones!

---------- Post Auto-Merged at 21:54 ---------- Previous post was made at 21:50 ----------

If you can't figure out which one you have remember that the linked out terminals are for a room stat and the LR terminal is basically the demand from the stat (or clock)

 

[steptoe]

Dave,

I dont know the boiler you have but Noz may well be correct,

a lot of boilers ask for volt free when they actually simply send a 230v signal out and simply want 230v back,

fire up the boiler and stick your voltmeter on the terminal and see what you are getting,

if it is 230v then simple forget about the feed out and take a switch live back to the switched side of the terminals.

 

[kev2632]

hello prodave could i ask you a question about this scenario you had here? i have something similar is that okay ??

 

[ProDave]

Post your question here and we will see if we can help

 

[SLIPSHOD & SLAPDASH]

I know this is an old thread but Steptoe has a valid point it probably was 230v contact, anyhow you could  easily fit a battery powered programmer that have clean contacts. These were designed to replace/upgrade a room stat to a timer. Alternatively many programmers have the motor terminals wired separate to the relay outputs, you would normally fit links between but in a case like this feed the motor from a local supply and the relay outputs would switch the boiler.