Timed circuit to replace a broken boiler timer.

Thread Starter

James1098

Joined Oct 18, 2021
3
Hey guys,

I'm trying to create a timed circuit that will replaced the broken timer on this boiler.

The timer will dictate when the middle knob will be turned from it's current position (off) to where the 50 mark is.

My initial idea was to use a 12v relay, timer and some kind of motor/actuator to physically move the knob (this is the only way to turn the radiators on and off). I can attach something to the knob that can be driven via motor or actuator.

I'm struggling to something to move the knob. I've looked at linear actuators but it seems overkill for the use-case.

Any ideas?

PXL_20211018_132043705.jpg

Thanks!
 

Thread Starter

James1098

Joined Oct 18, 2021
3
What did the broken timer do?
Why not replace that instead of trying to kludge something to turn the knob?
That was obviously my first thought. Someone came to look at the boiler and said that it would require the whole boiler being changed. It's not an option to just replace the old timer as far as I'm aware.
 

LesJones

Joined Jan 8, 2017
3,571
I am not clear why you can't just replace the faulty timer. I can't understand why you now need to rotate the set temperature knob knob to zero to turn off the heating. If you post the installation manual for the boiler it will help us to understand your problem.
Is the room temperature sensor internal to the boiler or is it mounted remotely ?. (I am guessing that the set temperature control is just a potentiometer and the actual sensor is a thermistor. Is this guess correct ?)

Les.
 

LesJones

Joined Jan 8, 2017
3,571
Timers that look similar to the one in your picture are available on ebay. They are available to work on 12 volts DC and 110 or 240 volts AC. I have one of the !2 volt DC versions of the timer and the round part is 60 mm diameter. This is a link to one seller on ebay for the 12 volt DC version.

NOTE. I originally pasted in the wrong URL for the link. I have corrected it now.

Les.
 
Last edited:

Thread Starter

James1098

Joined Oct 18, 2021
3
I am not clear why you can't just replace the faulty timer. I can't understand why you now need to rotate the set temperature knob knob to zero to turn off the heating. If you post the installation manual for the boiler it will help us to understand your problem.
Is the room temperature sensor internal to the boiler or is it mounted remotely ?. (I am guessing that the set temperature control is just a potentiometer and the actual sensor is a thermistor. Is this guess correct ?)

Les.
Hey Les,

Manual is here.

From scanning it quickly I think your guess is correct.

In regards to the clock:

This image is taken from page 21 of the manual, describing the installation of the clock.

1634569173400.png

I just had a look at the back of the clock in the boiler, the connectors to terminals 3 and 5 (terminals on the clock are, left to right, 1 2 3 5 this online manual doesn't denote that but my paper one does :) ) are unplugged and taped up to the side. The timer currently shows all symbols on the display and this doesn't change when I turn off power to the boiler.

When the guy came to look at it 18 months ago or so he gave a reason as to why the timer wasn't working and why it couldn't be replaced but I can't remember for the life of me what it was.

Right now to turn on the heating I move that middle knob to 50 or so. This is all manual and I thought it might be a fun project to automate this, essentially replacing the function of the timer that I should have.

Hope this gives more context?
 

LesJones

Joined Jan 8, 2017
3,571
This is a picture of the back of the timer that I have.
181021.jpg
You can see that terminals 4 and 5 on the timer are the relay contacts in the timer.
Terminals 1 and 2 are the power to the timer. If the markings on your timer are similar to mine the supply voltage is indicated with a mark in the box next to one of the voltage options. If not measure the voltage between the terminals of connector X2 on Fig.31 If you decide to replace the existing timer this will allow you to select the correct version of the timer.

If you decide to use an external timer just connect it's relay contacts to terminals 1 and 2 on connector X4. (NOTE THE TIMER THAT YOU USE MUST JUST HAVE CONNECTIONS TO IT'S RELAY CONTACTS. IT MUST NOT HAVE THESE CONTACTS CONNECTED TO ANY SOURCE OF POWER.)

Les.
 
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