replacing the timeswitch on my gas ch boiler with modern one

[tredman70]

Hi Ihave a 25 yr old Thorn Marathon 80/100c gas ch boiler and need to replace the built in CH/HW timer with a wall mounted modern timer - any tips?

 

[stem]

Take advantage of the boiler scrappage scheme and replace it. You are running a 'G' rated (65% efficient) appliance and wasting the earth's resources and your money.

To figure out how to replace the timer would require an examination of the boiler, or a wiring diagram of it. I would be surprised if anyone could find the latter due to its age.

 

[MrGassafe]

Your boiler manual and wiring diagram can be found on the Parts Arena site

http://www.partsarena.com/baxi/system/index.htm

Should be able to work out external programmer wiring from this.

 

[Lincsbodger]

Take advantage of the boiler scrappage scheme and replace it. You are running a 'G' rated (65% efficient) appliance and wasting the earth's resources and your money.

This is a myth.

I have a 30 year old Glow Worm 45-60 to heat the 5 rads in my bungalow. Ir works fine, its simplicity itself, all the parts are cheap and available. The cost of replacing it will be £2000+, the replacement boiler will be a nasty thinly made modern thing that will be corroded away in 5 years tops, requiring regular replacement, whereas the old one will chug along for at least another 20 years.

I dont believe (and feel free to show me the maths to prove me wrong) that the cost of running the old one in terms of carbon impact and monetary cost, outweighs the cost of making two or three new ones and running them instead, especially if you weigh the simplicity of the existing system with the potential complexity (and correspondingly expensive to fix problems) of a new one.

:

 

[stem]

Simples! Old boiler 65% of gas used heats radiators/water, 45% goes out of the flue. Wasted gas, a natural resource, also produces more CO2 to boot, plus cast iron heat exchangers made in foundries.

Untitled

• stem
• 19 Mar 2010
• 1

New boiler 90% of gas used heats radiators/water, only 10% out of the flue.

Ok, you may want to argue with the efficiency figures but as I don't have the capability to work it out and I don't imagine you do either, we have to go with the figures we are given by others.

I suppose with your line of reasoning, you are still driving a 1980 Ford Escort, nice and simple, uncomplicated, thirsty and oh yes, parts are readily available.

 

[stem]

Well done with the diagram MrGassafe. Back to the OP then. Here's a marked up wiring diagram showing a new programmer in place. I hope you can read it OK, the quality of the original wasn't great.

Untitled

• stem
• 19 Mar 2010
• 1

It would be best to remove the existing programmer plug and socket from the boiler terminals and wire the new programmer direct to the boiler in place of them. The control wires are shown in blue, but they are actually lives (I was running out of pen colours)

From the boiler terminals:
Connect Earth to new programmer earth terminal
Connect terminal L to the live supply to the new programmer
Connect terminal N to the neutral supply to the new programmer
Connect terminal 1 to the "hot water on" terminal on the new programmer (this operates the boiler gas valve via the thermostat)
Connect terminal 2 to the "central heating on" terminal on the new programmer (this operates the pump)

The link between terminal L and 1 should already be missing.

Use heat resistant wiring.

When choosing a programmer get one suitable for a gravity based hot water system that doesn't allow the central heating to be on without the hot water being on. (It's not crucial but it would mean that if you did select heating only, the pump will run, but the boiler won't fire up)

This assumes that the system hasn't been upgraded at some point in the past and converted to a fully pumped system with motorised valve(s)

Hope that helps, let us know how you get on, or if you need any more help after you have obtained your new programmer. Some programmers might require links across some of their terminals, depending on type.