Just before the Festive Season we had a power cut and our Honeywell ST699 central heating timer reset itself. I imagine there is an old NiCad battery in there which has popped its clogs. I am thinking that this would be a good time to replace this 24 hour timer with a 7 day timer.
I would love to hear about peoples' experiences changing their timers. What timers are good? Did you fit it yourself? Was it a nightmare or was it quite easy? Is there someone you would recommend we get to come and do this for us? (We live in Soham - that is between Ely and Newmarket, East Cambs).
We've got a programmable thermostat that combines timer and stat. We can set different temperatures at different times. There's a number on the market. Ours is battery opperated which reminds me, it's due for a change.
Hmm. I hadn't thought of that. It sounds like it might be a bit too sophisticated for our requirements, though. I'll bear it in mind for the future. At the moment, I'm looking to get something done for the short term in case of the combined effects of a power cut, a cold snap and us being out - so our pipes don't freeze and burst.
the unit. It looks like the battery is a doddle to change. It appears that the 3/V150H Ni-MH VARTA Mempac Range battery from the following website will do the job...
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perhaps, out of laziness, I'll just settle with the new battery for the moment...
=2E..only trouble is - when I click the 'add to cart' button on the page I get a blank page in return. Is this a Firefox incompatibility - or is this supplier defunct? I'll try ringing them on Monday - unless anyone knows of anywhere in the Ely, Newmarket, Cambridge area where I could pick up one this afternoon?
Not really - the two work very well together. The ability to set different temperatures for parts of each day and except the weekend if needed are a big energy saver. And the timeswitch will still switch things on and off totally if that's what's required.
The battery failing shouldn't stop the thing working - it's only a backup for when the mains fails.
>I have actually just summoned up the courage to flip off the top of
I use Firefox - but also have IE installed for just such eventualities. There are many times when such sites (online purchasing) will not work with Firefox but are fine with IE.
I've just bought one from CELL PACK SOLUTIONS LTD (capitals courtesy of cut and paste) whose web site is Firefox friendly.
Mr Gee told me over the phone that he had the batteries with posts attached for soldering into PCBs. I need one with no posts. It slots into a holder on the PCB. I would have definitely got one from Gee's if he'd had the right type. Looking at Maplin's web site , they only do the batteries with posts, too.
The Honeywell ST699 is just a simple 24 hour timer with one or two on/off periods a day. I believe it's still available for around £50 if the problem is not the battery.
Will your system allow you to have the heating on without hot water?
There are better timeclocks around that allow more on/off cycles a day or different times for different days of the week (eg 5/2 or 7 day). Possible examples:
Honeywell ST9400C... £51
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"The ST9400C is a 7 day two channel programmer designed for individual control of both hot water and heating and feature the LoTT display, it also offers up to three "on" periods per day. Additionally each day may be programmed differently. This programmer may also be configured as a Mini Programmer for older gravity - circulation stored hot water systems."
Danfoss FP715Si..... £40
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FP715 Si two-channel full programmer has separate Heating and Hot Water outputs operating on completely independent time bases for maximum flexibility. The FP715 Si can be configured by the installer at time of installation to provide 7 day, 24 hour, or 5 day/2 day operation and to provide either 2 ON/OFF's or 3 ON/OFF's per day, allowing the time control to be tailored to match the specific requirement of the consumer.
In that case, a programmable room stat would do some of that nicely. (Just swap it for the current analog stat). As far as the main timer is concerned, the CH is on constantly - with the actual timing being done by the programmable stat. Typically these allow you to specify 6 temperature changes per 24-hour period which - if you wish - can effectively be three on/off periods. When you want the heating on, you specify the required room temperature (which can be different at different times of the day if you wish). When you want it off, you specify a temperature (say 5 degC) which is low enough that the house will not normally fall to it between heating periods. However, if the temperature *does* fall that low, the heating will come on to prevent everything freezing up.
Some programmable stats have other gizzmos such as:
Optimum start. You specify the time by which you want the house to be warm, and the stat works out when to turn the heating on.
Party mode. Allows you to override the settings for a specified number of hours in order to, for example, keep the house warm longer when you're having a party. Can also be used for saving energy by lowering the temperature for a few hours when you go out shopping etc.
Holiday mode. Turns the heating off for a specified number of days (mine does up to 99) and then returns to the normal programme. Useful if you want to come home to a warm house without leaving the heat on all the time when you're away. Also acts as a frost stat while you're away, and will turn on the heating to prevent freezing if necessary.
A programmable stat won't help in the event of a power cut of course - except that its timer will be battery operated, so will continue to tell the correct time. Are you considering a generator to power the CH's electrics? That's quite do-able when you're there to plug it in and start it up - but starts to get complicated (and expensive!) if you want it to be fully automatic.
Heh - no! That is far more sophisticated than I want. Currently, a power cut causes the timer not only to forget the time but the heating/ hot water settings. Hence, just a short power cut will cause the heating to shut down completely until someone resets it.
I've got a battery on order now. I'm hoping that once I've installed it, the central heating will once again work as it used to and come back on and work normally after a short(ish) power cut.
Thanks for the info about programmable thermostats. I'm not sure our system is sophisticated enough to benefit from one, though. The one place in the house which gets too hot is the kitchen and that is the only room that doesn't have a radiator. Most of the other radiators have thermostat valves. We don't have any wall thermostat.
snip the leads off (If you're deft, you can get cutters in behind the post and turn the post off). The hardest part is often when the old battery corrodes itself into the white plastic sleeve - you don't need it
Just make sure you insert it the right way round
The ST699 has a unique backplate, so replacing it with something else is a rewiring job
Why is that messy? Assuming that the original timer allows HW and CH each independently to be set to Off, Timed, or Constant, you simply set HW to timed and CH to Constant. Then as noted earlier, the programmable stat does the actual timing for the CH - as well as providing a number of other functions which are useful for space heating but not necessary for HW.
If you were starting from scratch you might do it differently - with a single channel timer for HW, and with the programmable CH stat fed directly off the FCU - but when adding a programmable stat to an existing system, the scheme which I outlined is by far the easiest to implement.
I have installed a new battery in the old central heating timer, now.
I took the cells out of the green plastic sheath they arrived in and put them in the original beige plastic sheath (with the locating pin) that was in the unit. I didn't have to chop any legs off because the battery I bought didn't have any.
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