Wireless Thermostat -Honeywell CM927 or Drayton Mistat P710?

[JustinS]

Dear all,
I'm looking for a bit of unbiased advise on choosing a new thermostat for my house, and wondered if you guys could give me some opinions pls before I bite the bullet?
I have a smallish 3bed semi that is 3 yrs old with fully trv'd rads with a Potterton SL12 boiler, Horstmann Centaurplus C27 and HRT3 stat.
So you wouldn't call any of it top of the line, but basically it all works.
My problem is the HRT3 seems to have a mind of its own, on and off at will and seems to shoot way past the set point, walk past it and it will tick on, knock the wall or turn on a light switch it comes on too, it's just mad! But it seems like this by design, I've changed it and it doesn't seem to make any difference so I've come to the conclusion it is just cheap and a bit nasty and not in anyway accurate. I read it had some resistor that heats up inside to turn it off to increase comfort, or something like that!
So, the commissioning sheet for the house says the water temp set on the boiler is 77degs, but I find because of the thermostat the house doesn't heat and stay comfortable.
The boiler will light for a max 5mins every 20 mins unless you up the temp on the stat, like it can't keep up, thermostat is located in the hall a foot away from the front door so probably the coldest place too, but a rad (not trv'd) is only across the hallway width.
So having read about the TPI on the cm927, I was thinking this could in fact be a good idea for us, and maybe a min run time would help us too, we don't ave any pump overrun either.
But then again the Drayton P710r I think has selectable tpi or just on/off so this could avoid the cycling that others members don't like if the TPI wasn't the best solution.

Also I'd need a perm live to the receiver of either unit, I'm thinking this could come off the lighting circuit as its directly above a switch for the porch light, do you guys see any problem with that or should it be located in the airing cupboard with the wiring centre?

Any suggestions or others I might have missed?

Thanks a lot for any replies, just don't want to make the wrong choice.

Cheers

Justin

 

[Whitespirit66]

Well, if you can take a completely biased opinion, I don't like TPI. Some of my customers don't like TPI. Certain systems don't seem to like TPI. Not much point going for the Honeywell, as it has TPI, but so does your Horstmann stat.

Some of the problems that you describe could be because of TPI, but I'm also wondering if your stat is too close to the hall rad and drafty front door. TPI relies on learning about your system and property's heat up time and thermal loss. The location may poss confuse this and would also be unsuitable for traditional stats.

Perhaps first try locating the stat into your lounge and leave the TRVs on the ras(s) in there on max. I'm not sure how good Horstmann stats are as I don't have a lot to do with them.

The Drayton Mi range of programmers and stats is my preferred choice for installations. Unlike many others, the Draytons are selectable between TPI (they call it chrono proportional control) or operating as a normal stat.

 

[JustinS]

Thanks Whitespirit,
Sounds like the Drayton will pretty much do anything that can be asked from it then!
The Horstmann is really super basic, I'm thinking your right and half the switching it is doing is because of its mounting location, and the rest is analogue control that's simulating TPI. If you take a look on screwfix or google it lots of people describe the same behaviour so I think it's inherent, it's less than a tenner too!

Can I ask if any of the Drayton programmers are particularly suited or what would you normally team this stat with?

All the best and thanks

Justin

 

[D_Hailsham]

Do you have a multimeter and know how to use it?

If so, check that the HRT3 has been wired correctly.

Turn the knob to the maximum temperature position (35°).
Insert the blade of a screwdriver in the fissure between the knob and the top cover.
Use the screwdriver as lever to remove the knob.

Remove the cover retaining screw situated behind the control knob.
Then press lightly with a screwdriver on the fixing hooks either side and remove cover.

WARNING: TERMINALS MAY BE LIVE

Replace knob and turn stat to minimum.

Check that there are three wires connected to 1, 3 and 4. If no wire to 4, that is the cause of your problem: the anticipator resistance is not connected. If there is no neutral wire hidden behind the stat, changing to a new stat would be a good idea.

If terminal 4 is connected, you need to check that the wires to 1 and 3 are the correct way round.

Set timer to permanently on.

Measure voltage between 1 and 4 (meter set to AC volts).
If you get 240Vac the wiring is correct.
If you get 0Vac, the wiring is wrong.
Check by measuring voltage between 3 and 4.
If this is 240Vac, the wires to 1 and 3 need to be swapped.
TURN POWER OFF before swapping the wires.

Replace cover and knob.

If problem still occurs, change the stat.

If you want to install a RF stat, the best location is in the cupboard with the wiring centre, but check for good communication between the tow parts of the stat.

 

[D_Hailsham]

Not much point going for the Honeywell, as it has TPI, but so does your Horstmann stat.

The HRT3 does not have TPI; it's an old fashioned mechanical stat with an anticipator.

 

[Whitespirit66]

Can I ask if any of the Drayton programmers are particularly suited or what would you normally team this stat with?

All of the Drayton MiStats room stats are wireless, so this will give some flexibility for stat's location. If you are happy with your current programmer, you can keep and just replace current room stat with MiStat wireless RF.

http://www.plumbnation.co.uk/site/drayton-mistat-wireless-room-thermostat---receiver-mn110r/

If you want to upgrade the programmer, you can fit the Drayton T720R, which is a twin channel (hw and ch) programmer with built in wireless room stat receiver and the remote room stat.

http://www.plumbnation.co.uk/site/drayton-mitime-rf-pack-2-t720r/

 

[Whitespirit66]

Not much point going for the Honeywell, as it has TPI, but so does your Horstmann stat.

The HRT3 does not have TPI; it's an old fashioned mechanical stat with an anticipator.

Yes, apologies. Got my models mixed up.

 

[JustinS]

Thanks everybody for the replies.
Super helpful of you both.
I made a quick check with a meter again just to be sure, and I have the following:
1= 240v switching from the programmer ch on/off (brown wire)
2= not connected
3= switched 240v when the stat led is on (call for heat) (black wire with a brown sleeve)
4= neutral (grey wire with a blue sleeve)

And tucked behind is a green/yellow sleeved earth that's not connected, but insulated.

Seeing as this is the second HRT 3 I've had as I changed it already thinking the switching was way too much, and the fact you only had to touch a side of the dial for it to come on, only for the new one to be the same too, I think it is just the way this unit is!

All I can see that I'm missing to change it over in the present location to the receiver is the permanent live, as the live I have here is from the programmer, to use it is have to set the programmer as "always on" or add a live.

Many thanks everyone, I'm still thinking the best solution is to look at a different stat and getting it into a different location could well be a good idea too.

Cheers and thanks

Justin