Old CH, new (wireless?) stat?

[T i m]

Hi all,

I'm trying to get the feel of the pros, cons and otherwise of a CH question for an elderly neighbour we keep an eye on.

She has an existing and fully functional CH/HW system but there is no room stat, just thermostatic rad valves (that apparently 'don't work and have been replaced once already').

Her son sets the timer up for her to give HW once per day and CH twice but I think something more 'temperature managed' might be more suitable, as she's now no spring chicken.

So, the question is, 'how easy and what would be best' if we wanted to add a room stat to this setup please?

Potterton Netaheat Electronic B/F CH boiler. Honeywell: Timer ST799 (or looks just like one)

3 Position Diverter Valve (L641A1005) Cylinder Stat. (L641A).

Grundfos pump (that I replaced a while back with the help of some good folk here). ;-)

There is also a junction box.

So, would you be able to use an addon Wireless stat with this setup or to give more flexibility, would it be best to replace the Timer with one that can accept a wireless stat directly (if such exists etc).

I think I understand that some of this new gear gives quick access to background CH temperatures / living temperatures etc and as long as it is reliable I can't see her needing to touch it one 'programmed (as long as she can manage the room stat etc (she's actually not bad and even uses the PC I gave her quite a bit)). ;-)

Oh, whilst she's not made of money I don't think she would mind spending the right money to get something

Cheers in advance,

T i m

[A.Lee]

It's an easy job. Salus are the cheapest, generally £35ish, Niglon do a nice one, though I've only ever seen it in my elec wholesalers. Honeywell are the best, but double the price. They do do one with an old style dial guage (Y6630D), which is generally more suitable for older people who dont like pressing buttons and reading LCD displays.

Wiring, just think of the stat as a switch, one wire in, one out, so the link from the CH on, on the programmer, goes to the stat, and where it was terminated before, goes to the other cable from the stat.

With wireless you'll also have to add a permanent live and neutral to power the base station. All very simple, and they'll save around £50 a year on their gas bill typically.

[fred]

In article , T i m writes

I have done similar for an elderly rellie and used a Honeywell CM927 wireless stat which sits beside her favourite chair in the lounge. Basic programming is 2 periods of full heat (morning and evening 20degC or so) with a setback to 18degC during the day and 17degC overnight).

The Honeywells are so easy to use that it's no challenge to bump up the daytime temperature a couple of degrees if she's feeling a bit cold.

I perform seasonal programming twice a year to balance comfort levels in the colder months.

That said, I don't like Honeywells myself as IMV they cycle the boiler excessively (6 cycles per hour default, can be reduced to 3 per hr at install). I don't like this as even if you go on holiday and set back the setting to 10degC it will cycle the boiler (and controls) excessively to maintain 9.75 to 10.25 pointlessly when 9 to 11 would do just as well.

I've also had 2 installs of the CM927 lose pairing (stat to receiver comms) every time the power is cycled which is recoverable but bldy annoying.

I currently use a cheapo Salus programmable wired stat (modified for remote sensor operation) which is fine for me but the setting is less than intuitive. I use it as it employs simple on-off control, marginally less tight temp control but the boiler only cycles once and hour or so.

John Stumbles has done a recent review of the Drayton MiStat wireless stat which might be of interest and can be programmed to proportional (cycling) or on-off:

You don't need a timer at all (for CH) if you have a programmable stat although you can keep it and set it to 24hr heat.

[dennis]

Basically it replaces the timer on the ch side. You program the times you want it on and the tempreture it switches on and off at. Put the remote bit in the living room and turn the rad stat on full.

[Dave Liquorice]

Agree I guess she is home most of the time so "morning" and "evening" isn't really suitable for the CH. A wireless programmable thermostat would offer different temperatures through the day. Ours (Danfoss TP7000-RF) is at 15 C overnight, goes up to 18.5 C between 0700 and

1600, at 1600 it goes up to 20 C, back to 18.5 at 2300 and 15 later still. Suits our pattern of activity, ie busy moving about during the day, asleep watching the telly in the evenings. B-) It has "nudge" buttons to temporally adjust the temp up or down, it reverts to the programmed temp at the next timed event (there are 6 events/day).

As the system can be programmed to have different HW and CH times I'm going to assume fully pumped and not gravity HW. Get a wireless programmable stat and place the Rx near to the wiring center. It will need permanent mains and a couple of extra wires to carry the switched feed. Two T&E's will do that, suitably sleeved for the one carrying the switched feed).

The simplest control wiring is to take the CH switched from the programmer, to the Rx'er and from the Rx "make for heat" to the same place as the programmers feed was just removed from. You then set the programmer to permanent on for the CH and the programmable stat takes over.

[alan]

Site the sender unit in the room used most for seating/watching TV and also disable the thermostatic rad valve (leave on highest temperature setting) in that room to let the thermostat do the work of regulating the temperature.

[Dave Liquorice]

Yep, puts unnesscary cycling on the valves (who makes the most common motorised valves? Hum Honeywell...). The Danfoss TP7000 is very similar feature set to CM927 but can be set to on/off rather than proportional.

[DerbyBorn]

"Dave Liquorice" wrote in news: [e-mail]:

Isn't cycling a function of the boiler thermostat rather than the room stat

- unless the local radiator is having too much influence over the room stat.

[Roger Mills]

As others have said, you simply need to break the CH connection between the programmer and motorised valve, and insert an electronic stat in it.

It's not totally clear from your post whether it's a W-Plan or Y-Plan system. You refer to a "diverter" valve, which usually implies W-Plan (i.e. switches between HW and CH - usually with HW priority, without the ability to send primary circuit water to both at the same time). But you might have meant "3-port mid-position valve" which can run either HW or CH *or* both at the same time - in which case it would be a Y-Plan system.

You'll see what the wiring for each of looks like on pages 3 and 4 of this document:

As drawn, these are both shown with mechanical thermostats - which need a neutral connection for the return from the accelerator heater. If using a programmable stat, just ignore the neutral connection. You should, be able to wire a stat into the junction box. If the system is wired conventionally, the stat will need to be between 4 and 7 for a W-Plan or between 4 and 5 for Y-Plan. In the absence of a stat, you'll find a bridging wire between the appropriate terminals - which you'll need to remove.

As far as timing is concerned, it's easiest to set CH on the existing programmer to "Constant" (permanently on) and let the programmable stat do the actual timing. Let the existing programmer continue to time the HW.

[fred]

In article , DerbyBorn writes

Any situation where a boiler a boiler repeatedly switches on and off for short periods is by definition cycling (or short cycling) but there can be a number of causes.

One scenario is as you describe, when a system is up to temperature but there is no room stat to say, 'enough guys, stop now' so the boiler cycles pointlessly on the boiler stat.

The other is deliberate cycling of the boiler and controls by a control system employing proportional control. By monitoring temperature changes when the boiler is firing the control system estimates that the boiler will need to fire for say 12mins per hour to maintain a given temperature. To smooth out temperature fluctuations, the control (proportional stat) decides instead to fire the boiler to fire for just

2mins, 6 times per hour. This sounds like a good idea and results in tighter temperature control but it also results in mechanical controls (like zone valves) operating 6 times as often (and lasting 1/6 of the time), boiler ignition circuitry operating 6 times as often and arguably in less heat being delivered where you want it (pipes passing through halls and landings get hot quickly but rads in the rooms where you want the heat are slower to reach temperature).

IMV a long slow burn delivers more heat where you want it and is less hard on the controls. This can result in a little temperature overshoot but I can live with that.

[Jim K]

won't that potentially mean the rest of the house is cold(er) than perhaps preferred?

Jim K

[PeterC]

Just turn up the TRVs on the other rads.

[T i m]

Yes, so firstly may I just say a big 'thanks' to all who responded with what looks like a general agreement on what and how. I'm replying here but it is really to all (of course). ;-)

Ah, sorry. I could have added I believe the L641A1005 is a 'Y plan' (from the label).

Thanks very much as 'a picture speaks 1000 words' n that. ;-)

Understood. (Googles 'accelerator heater' and finds it was a technique used to help reduce short cycling on bi-metallic stats).

Check (Y plan so 4 and 5 as noted on the diagram).

Check (And something I can easily investigate).

Nope, that all make perfect sense, thanks. ;-)

I do 'get' the points against the Honeywell's and 'system cycling'. I can see what they are trying to do (smaller hysteresis / overshoot) but agree re the additional load on the system and components. However (devils advocate mode - / on) I guess *if* this renders a more constant temperature it could be worth the shorter life expectancy of the parts, depending on how sensitive you are to such temperature changes and the life expectancy of the occupants etc (dam / off).

Luckily this particular lady comes from the 'no heating, only Lino in the bedroom and put some more clothes on if you are cold' era and after only having the heating on twice a day, *anything* that improves on that will be seen as a big plus. That said, she really isn't very well right now (ulcerated legs) so (as mentioned here) being pretty well housebound makes this much more pertinent.

I'll take a list of the stats referenced here to our local plumbers merchants, see what they have in stock and if I can get any feel of how they might appear to our 'nice old lady'. As I mentioned, whilst she's not the most technical now, she did work for Thorns in the PCB manufacturing arena for some time, and seems to be able to get on reasonably well with the PC I built her (once she has done something a few times) so I don't think we *need* the most simple solution, *if* it removes a feature that would suit her current needs or a future one.

The only thing I have in the back of my mind is I'm not sure she would want the heating on at night. She's one of these people who generally turns everything [1] off at the wall so outside of possibly not wanting the heat on at all at night is the idea of something (especially the boiler etc) being on at night. Mind you, if the feature is there I presume you don't have to use it?

Thanks once again to all. It's all less daunting when at least you know the light at the end of the tunnel isn't an oncoming train. ;-)

Cheers, T i m

[1] That she can / knows about. ;-)

[fred]

I don't think that really achieves anything, TRVs just limit the maximum temperature, they can't call for heat themselves so they can't make a room hotter if the problem is the master control not remaining on long enough.

To get around this problem, the room with the stat always needs to be the last to reach temperature (and switch off the call for heat) and the first to lose its heat (so it can call for heat again).

If that room is a living room then this is a conflict of requirements as it is probably the one you want to be the cosiest little box.

You can slug the rate of temperature rise by slightly throttling the rads in that room and you can let it pass heat to the rest of the house by not tightly closing the lounge door.

Neither of these situations are ideal but it is about the best you can get if you want granny to have fingertip control of temp in the main living space.

And yes, all the auxiliary heat sources in a lounge (telly, people etc) distort the picture but it is a compromise. Obviously doesn't work if granny uses a gas/leccy fire in the lounge, then your stuck with TRVs and a stat in the hall as the master.

[dennis]

That's the big problem with a room stat and TRVs. There is no position where it will give complete control.

If you put it in the coldest place then it will sometimes turn off before the warm places are warm. If you put it in the warmest place then it will sometime not turn the heating on and other areas will stay cold. There is no single position that works all the time.

Weather compensation is an attempt to get around it by predicting possible heat demand which may or may not help depending on the building.

Putting it where the OAP spends most of their time is probably going to be best if there is only one stat as this is where you want to maintain the temperature and you do not want her getting cold while she is sleeping in the arm chair.

If you want to do the job properly you need multiple stats so you can demand heat as required, then you may as well zone it and do the job properly.

[Roger Mills]

That's easy enough to achieve with a programmable stat. Just set the overnight temperature demand low enough (say 5 degrees) for the heating not to come on.

Or, if you wanted to be *really* sure, you could set the original programmer to be on all day and off at night rather than permanently on, as I suggested earlier. [However, if the hot water doesn't have an independent timer, that might not work.]

[T i m]

Thanks for that but I was meaning more to do with the fact that it was still 'on' than it would come on (re people who unplug everything all of the time). As it is set now the boiler can't come on at all in the night.

Yes, if she does have an issue with this then that should be a solution.

I think it does. (I believe it's a Honeywell ST799).

Another quick question that has come up from the good answers here if I may. On a TRV, should turning it down to the lowest setting turn it 'off'? If so and if these don't, what could be the typical reason please? I ask because she suggested they 'never worked from new' (as in reduce the temperature in each of the rooms) and that they have been 'replaced once already'. Is it possible replaced the heads but it wasn't the heads at fault?

Another thought that crossed my mind on that ... she seems to keep all the internal doors open and the complaint was that it was 'too warm upstairs'? ;-(

I think I'll need to investigate all this closer (but I just wanted to check how the TRVs were supposed to work first).

Cheers, T i m

[chris French]

In message , T i m writes

Normally the lowest setting is a 'frost' setting, on the Drayton TRV4 I just fitted it is 8C. So unless the house is very cold, yes it should turn off the flow.

If the valve doesn't close down fully then it suggests some crud or scale on the valve seat maybe?

[Davidm]

I can confirm that the frost setting is about 8C, I learned the hard way. Last winter I was decorating my dining room, with the radiator removed and the TRV turned "off". Opened the french doors to let the dust out, and next thing I know I was paddling in dirty water. The room had cooled down and the TRV had opened.

Next time I WILL remember to remove the TRV head and fit the plastic screw cap they supply, which was burried in my drawer of plumbing bits.

[T i m]

Ah, thanks.

Well, whilst it could be I'm led to believe this is the case on all the rads and from new?

This is what she 'said' so I will have to investigate for myself.

So, with the house 'warm' (or above say 8 DegC at least ) the rads should go cold with the TRV set on the lowest setting.

Cheers, T i m