timer for central heating

Hi all,

We have an old timer (for an oil central heating unit) which no-one can use, so I want to replace it with an easy to use one.

Has anyone done this? Do you use a central heating person or an electrician? Is it an expensive job?

Any details welcome!

I came across this site lately and it may help.....
[broken link removed]

Haven't gotten around to it yet but I'm planning to replace my mother's old/broken rotary timer and swithes (one each for OFCH pump and boiler - not sure why they were separately switched in the first place!) with one of [broken link removed] - about €40 from Maplin. You can probably get similar units (possibly cheaper) from any electrical wholesaler. The manufacturer's website is [broken link removed]. Obviously isolate things at the fuse/switch board before working on the wires etc. If you don't know what you're doing then get a qualified electrician on the job.

I always fit one of these guys' ones: http://www.horstmann.co.uk/downloads/ElectronicDocuments/Central-Heating/ChannelPlusH37XLDatasheet.pdf made by http://www.horstmann.co.uk/ Nearly every plumbers merchant in Ireland sell them.

With a 3-channel unit, you can have separate timings for upstairs/downstairs/dhw (providing it's plumbed to match, that is........).

If it's not plumbed to allow separate controls, just buy the two-channel version.

Just to tag onto this thread - in relation to my mother's OFCH system (fitted probably more than 30 years ago at this stage!) there is a panel in the dining room with the (now broken) rotary timer (which was never really used that much anyway), some fuses separate from her main fuse/switch board, and also two separate switches - one for the boiler/burner (installed in a shed outside) and one for the pump. Is there a good reason for the separate switches? After all why would you ever switch one or other of the pump/burner on without the other? Surely doing so might cause damage - or would it?

Spoke to somebody about this and he explained how the pump often runs for longer than the burner (i.e. for a while after the latter has switched off) in order to continue circulating hot water through the system and (in some cases) to avoid water boiling off in the burner and damaging the heat exchanger (?). Anyway since my mother's system has worked fine for 30+ years with both switching on and off at the same time I left well enough alone. Fitted the Maplin timer switch mentioned above and it all worked out fine. Just needed to understand the existing wiring into the original timer unit and then attach things similarly with the new one. Job's oxo!

ClubMan said:

the pump often runs for longer than the burner (i.e. for a while after the latter has switched off) in order to continue circulating hot water through the system and (in some cases) to avoid water boiling off in the burner and damaging the heat exchanger (?).

Click to expand...

It is relatively safe with modern burners/boilers to have the pump wired in line with the burner as there will be a high limit thermostat in the boiler which will cut the power to the burner in the event of serious excess heat.

You will find when the pump is wired seperately that there is a thermostat on the flow very close to the boiler which runs the pump. If that thermostat is in place you can leave the pump switch on and it only runs when the hot water in the flow is up to temperature.

davidoco said:

It is relatively safe with modern burners/boilers to have the pump wired in line with the burner as there will be a high limit thermostat in the boiler which will cut the power to the burner in the event of serious excess heat.

You will find when the pump is wired seperately that there is a thermostat on the flow very close to the boiler which runs the pump. If that thermostat is in place you can leave the pump switch on and it only runs when the hot water in the flow is up to temperature.

Click to expand...

Thanks - only saw your reply now. However the system (including burner) in this case is of c. early/mid 70s vintage and yet it was always wired such that the pump and burner were switched simultaneously. It's survived this long so I left well enough alone. She also got the burner cleaned/serviced recently. Your man said it was the dirtiest he'd ever dealt with (!) but it was fine and the system is still going strong.