New Heating Timer

[LBOCS2]

Who should I be contacting to install a new timer for our central heating? A spark? Gas safe engineer? Boiler maintenance person?

We currently have an extremely old baxi back boiler with correspondingly aged analogue timer which is on its way out - it doesn't switch off reliably and I've had to run it the wrong way around on the timer because of the way the on/off switches work, plus they're extremely stiff so I can't always change the timings.

I'd like to replace it with a standard digital one - nothing fancy or requiring stands in different rooms or anything like that, but that I can program the heating and hw to come on separately and change the timings depending on the day. I had a Nest engineer over before and he said he couldn't fit the hive timer-digi-thing because there wasn't a suitable power supply to the timer connection and it couldn't be run because it would involve pulling the boiler out of the chimney breast. Has anyone had any experience of this? Is it even possible to change them without completely upgrading my very old but reliable and well serviced boiler system?

[PigletJohn]

If you already have a room thermostat, you can put a programmable thermostat in the same place, using the same wires, with great ease. It includes the heating timer.

If you have a programmer on the wall near the boiler, which controls both the heating times and the HW times, you can change it for a modern programmer with great ease. Post a photo of your old one. Some will click straight in. If your system is very old it would be best to have a heating engineer fit it, because you may have gravity (unpumped) heating to the hw cylinder. Is it currently possible to have the heating on and the hw off?

Are you young enough to cope with a digital programmer with buttons and multiple options?

Honeywell and ACL Drayton are probably the two best makes, unless you want a Nest or something.

[LBOCS2]

Nope, it's not possible to have the heating on with the HW off - just the other way around.

I'm comfortable programming a new timer, that's not a problem - I do it for all my friends and my elderly relatives! I was looking at something fairly basic that just does the job really, as I don't see the need to spend a lot on it as we have a thermostat in the hallway and TRVs in most of the rooms which do the job of regulating the temperature.

I had a look online to see if I could find a straight faceplate swap timer but couldn't see one - found lots of wiring diagrams but nothing which would switch straight out unfortunately.

[PigletJohn]

OK then, you system is probably plumbed with gravity hw and pumped ch, so regardless of programmer, it will not be possible for you to have ch on and hw off unless you alter the piping and fit an extra valve and thermostat. It will make a small saving in gas during the summer, but probably not worth doing until you need to change the boiler. However with your system it is particularly important to lag the pipes between the boiler and the cylinder, and to give the cylinder itself extra insulation as it is probably a yellow or plain copper one.

If it was me I would turn your old control to CH permanently on, and fit a programmable thermostat in place of your old wall stat to control the heating. It incorporates a timer and allows you to set different temperatures for different times of day and days of the week if you wish. Honeywell CM907 is I think the best. Although it is preferable to have the wall stat in your main living room that does not have another heating source in it.

If you just want a better programmer, Drayton Lifestyle LP will be fine. I suggest the LP722, so you can set e.g. times different on different days of the week, perhaps you stay up late on Saturdays and get up early on Sundays, and have Wednesdays off. It has a switch on the back to select your gravity HW. It is one of the best-known so any heating engineer will be very familiar with installing it. It has the standard backing plate so if necessary you can unhook it and fit another. Don't get a programmer or timer of any brand with the "si" suffix.

[LBOCS2]

Am I turning it to HW&CH on all the time, or just CH all the time?

My cylinder is actually pretty new and is blue after our old one sprung a leak a couple of years ago. Everything is lagged in there too as I've seen too many cases of damp caused by condensation and am a bit obsessive about it!

Thanks for the advice about the thermostat, I'll have a look at the Honeywell as it definitely sounds like it'll do what we want it to do :)

[PigletJohn]

If you get a new programmer, you can set the CH and the HW times individually; but whenever the programmer says "CH=On" and the wall stat says "CH=On" then the cylinder will be getting heated, whether you want it to or not. That's just the way gravity CH works, unless you spend a few hundred changing it, which I wouldn't in your case.

With the programmable stat, you turn the CH programmer to Constantly On, and the thermostat will turn it on and off according to its timing and temperature settings. You leave the HW timed. If you seriously wanted or needed to, you could buy a new timer for the HW (e.g. if your old one fails completely), but you don't need a CH timer as the programmable stat controls CH times.

[PigletJohn]

Honeywell

CM907

There is also a wireless version, but wired are more reliable and will connect easily to your existing point.

[LBOCS2]

Ah, but I can't switch my old programmer to ch=on and hw=timed. My only options on the old programmer are for CH&HW/HW only, then whichever of those I've chosen is on, off or timed. So if I've got my CH&HW on constantly, and then the programmable stat is turning the CH on and off, does that mean that the HW will permanently be being warmed up? Because it keeps the towel rail on in the bathroom and heats up the bedrooms a lot if it's on all the time, even without the CH on.

[PigletJohn]

Then I think you would benefit from a new timer or programmer, or perhaps your heating engineer can have a look at the old one and tinker with it. Then at least you can set the HW timing.

The HW warming upstairs radiators will be due to unwanted gravity (thermosyphon) circulation. You could convert your system to fully pumped and fit a 3-port valve, but that would cost hundreds of pounds, or possibly fit an antigravity valve, but they are quite rare now as your design is very dated. If you have a trusted heating engineer, consult him. I would hesitate to spend much trying to update your old system. Read your Messages.

[LBOCS2]

Thank you for all your help PJ - as always you are a font of knowledge!