Honeywell CM927 - suggestions to settings?

[jem16]

I have just had a Honeywell CM927 programmable thermostat installed and was looking for suggestions as to the best way to use it for both comfort and efficiency.

I haven't changed any of the default settings yet - what do most people use for temperatures/timing? I know it's individual preferences but just looking for a guide.

Any other useful tips?

 

[D_Hailsham]

It is really a matter of personal preference and your lifestyle. Set the first time to when you get up and a temperature you feel comfortable with when washing, showering etc. If you work and the house is empty you could set the second time to when you leave the house and drop the temperature to say 10C. The third time is set for say 30 mins before you arrive home and the temperature for what you want in the evening. Setting 4 would be for night time, so you set the time for when you go to bed and the temperature for, say 10C. Although there are six time/temperature settings you can disable those you don't need.

I happen to be retired, so home all day, but I still use all six settings. 1 is wake up time/temp, 6 is overnight time/temp. 2-5 have the same temp as 1 and are spaced evenly throughout the day. This means that, if at any time we feel slightly cold and manually raise the temperature, it will revert back to the set temperature at the next time point. We can't forget to set it back.

Don't fiddle with any of the other settings.

 

[PEDANTICVINDICTIVEMAN]

If it's got Optimum start dont use it, the damn thing will have a mind of it's own.

 

[jem16]

It is really a matter of personal preference and your lifestyle. Set the first time to when you get up and a temperature you feel comfortable with when washing, showering etc. If you work and the house is empty you could set the second time to when you leave the house and drop the temperature to say 10C. The third time is set for say 30 mins before you arrive home and the temperature for what you want in the evening. Setting 4 would be for night time, so you set the time for when you go to bed and the temperature for, say 10C. Although there are six time/temperature settings you can disable those you don't need.

So 10C seems to be a good setting for night and out at work all day. I shall set it to that and see how it goes.

I happen to be retired, so home all day, but I still use all six settings. 1 is wake up time/temp, 6 is overnight time/temp. 2-5 have the same temp as 1 and are spaced evenly throughout the day. This means that, if at any time we feel slightly cold and manually raise the temperature, it will revert back to the set temperature at the next time point. We can't forget to set it back.

I wondered about that. That seems like a good idea.

Don't fiddle with any of the other settings.

I shall try not to!

Thanks for the suggestions.

 

[jem16]

If it's got Optimum start dont use it, the damn thing will have a mind of it's own.

I believe it has although default is off.

You don't recommend it then?

 

[D_Hailsham]

If it's got Optimum start don't use it, the damn thing will have a mind of it's own.

I have had Optimum Start turned on for four years and never had any problems with it.

Of course it has a mind of its own - if it didn't it wouldn't work.

 

[jem16]

If it's got Optimum start don't use it, the damn thing will have a mind of it's own.

I have had Optimum Start turned on for four years and never had any problems with it.

Of course it has a mind of its own - if it didn't it wouldn't work.

OK optimum start is when the unit works out when to come on to get the required temperature at the time you want it.

How do you find it works?

Normally if I get up at 7am on weekdays I set the heating to come on around 6.30am so it's a reasonable temperature for getting up. If I therefore set the temperature for 7am any ideas how long beforehand it would come on? Now I know that's perhaps a daft question as it depends on what the temperature has fallen to overnight but just a rough guide?

 

[D_Hailsham]

OK optimum start is when the unit works out when to come on to get the required temperature at the time you want it.

How do you find it works?

Normally if I get up at 7am on weekdays I set the heating to come on around 6.30am so it's a reasonable temperature for getting up. If I therefore set the temperature for 7am any ideas how long beforehand it would come on? Now I know that's perhaps a daft question as it depends on what the temperature has fallen to overnight but just a rough guide?

I don't know how you prove that it works. I just know that the house is always up to temp by the time I wake up. I have a well insulated house, so the overnight temperature never drops more than about three or four degrees. This means that the time the heating comes on rarely changes. It would be different in a house with a high heat loss.

My system is set for a wake up time of 0615. I know, from experience, that the rads are starting to heat up at about 0530, but not exactly when it starts up. You would have to connect some sort of clock/timer to the system to be able to prove that it does vary the start up time with temperature. The problem is compounded by the fact that hot water (I have a cylinder) comes on about the same time. So the time the boiler starts is no indication when the heating starts.

Don't forget that the boiler does not run flat out until the set temperature is reached. If it did, the house temperature would continue to rise after the boiler stops. The boiler starts cycling when the room temperature is 1.5 degrees below the set temperature. The cycle period is 10 minutes and the on/off ratio changes as the temperature nears the set value. The minimum it will be is one minute on and nine minutes off.

 

[jem16]

I don't know how you prove that it works. I just know that the house is always up to temp by the time I wake up. I have a well insulated house, so the overnight temperature never drops more than about three or four degrees. This means that the time the heating comes on rarely changes. It would be different in a house with a high heat loss.

Thanks - that's very helpful.

I think I'll just have to try out a few different possibilities and see what happens. I'll perhaps monitor the drop in temperature overnight (although middle of winter would be different perhaps) and see how insulated or otherwise my house is. The only place I have had a temperature guage has been the bathroom - temp can drop by about 5 degrees overnight there.

The problem is compounded by the fact that hot water (I have a cylinder) comes on about the same time. So the time the boiler starts is no indication when the heating starts.

I don't have that complication - I have a Combi boiler.

Don't forget that the boiler does not run flat out until the set temperature is reached. If it did, the house temperature would continue to rise after the boiler stops. The boiler starts cycling when the room temperature is 1.5 degrees below the set temperature. The cycle period is 10 minutes and the on/off ratio changes as the temperature nears the set value. The minimum it will be is one minute on and nine minutes off.

Is this true for all boilers?

 

[ianniann]

I'll perhaps monitor the drop in temperature overnight (although middle of winter would be different perhaps)

You can approximate using the temperature difference between inside and outside. Ten degrees colder will cool down (approximately) twice as fast as five degrees cooler. This is a tricky thing to measure though. Most likely what you'll be measuring is how warm your brickwork is since it is such a large thermal store. Even when you've heated inside to 21C for a few hours, much of the brickwork may still be at say 15C. Fairly quickly the room will cool to 15C and you'll think your insulation is rubbish. Then it will cool very slowly after that, which is your actual rate of heat loss to the outside.

Is this true for all boilers?

No. Kinda. It depends. Most (decent) boilers will turn down the burners themselves when the flow temperature gets near the setting you have on the boiler. They'll try to maintain that same flow temperature regardless of the room temperature and how close it is to the stat temperature. If they're lucky then they can maintain the flow temperature near the set level until the room stat switches the heating off completely. If they're not so lucky, or if you got a cheap boiler, then they will have to switch off the burners intermittently to avoid overheating the water.

With some control systems, the controller indoors will give the boiler more information than just on or off. It will say how hard to work based on how close the room is to where it needs to be. This can include the level of the burners and the temperature of the water in the radiators. Again, the boiler may be able to just turn down the burners or it may have to turn them off intermittently.

Most new boilers have electronics in place to stop them turning on and off too quickly. Regardless of what the controller might be saying, your boiler may have an anti-cycling setting that keeps the burners off for at least say 3 minutes before it allows them to fire again. Or it may hold them off until the flow temperature drops at least a certain amount. Usually its configurable and usually you won't have to worry about it, but conceivably those settings could fight with an intelligent controller. You may have to adjust other boiler settings to work properly with an intelligent controller, but this ought to have been done by the installer.

 

[jem16]

OK unit worked well yesterday, coming on and off when required.

However this morning heating did not start up. Room thermostat showed the little flame symbol, room temp was 17.5 and target temp was 21.

I went out to look at the boiler - it's in garage. No led at all on the relay box. Tried changing to manual and increasing temp but still nothing.

Eventually put the room thermostat to OFF and back to AUTO and green led came on and boiler fired up.

Any ideas about the problem before I call the installer?

 

[D_Hailsham]

I'll perhaps monitor the drop in temperature overnight (although middle of winter would be different perhaps) and see how insulated or otherwise my house is. The only place I have had a temperature guage has been the bathroom - temp can drop by about 5 degrees overnight there.

Buy yourself a Max-Min thermometer (about £10) from a DIY shop. This will enable you to monitor the highest and lowest temperature.

Don't forget that the boiler does not run flat out until the set temperature is reached. If it did, the house temperature would continue to rise after the boiler stops. The boiler starts cycling when the room temperature is 1.5 degrees below the set temperature. The cycle period is 10 minutes and the on/off ratio changes as the temperature nears the set value. The minimum it will be is one minute on and nine minutes off.

Is this true for all boilers?

This is not a boiler feature, it's the way the CM Series thermostats work; it's called TPI. The whole idea is to control the room temperature more accurately than the traditional thermostat which keeps the boiler running flat out until the set temperature is reached.

The boiler goes off, but the house continues warming up due to the heat remaining in the radiator; so someone turns the thermostat down a degree or two; so the house then cools down too much; so the thermostat is turned up again; and so on, ad infinitum.

Modern electronic thermostats can measure very small changes in temperature and so can react quicker. You will find that you feel more comfortable at a lower temperature and that the radiators feel cooler.

I went out to look at the boiler - it's in garage. No led at all on the relay box. Tried changing to manual and increasing temp but still nothing.

Where is the relay box getting its power, i.e the connections to L and N? It must be from a permanent supply.

If that is OK then did you check the communication between controller and relay box before fixing them in position?

Do you have a frost stat?

What happens if you carry the controller into the garage?

 

[jem16]

Where is the relay box getting its power, i.e the connections to L and N? It must be from a permanent supply.

It's getting power from the same switched socket that powers the boiler.

If that is OK then did you check the communication between controller and relay box before fixing them in position?

I left that to the installer. As far as I'm aware the relay box was fixed into position next to the boiler then the controller was switched on. As it all seemed to work that was all that was done. I don't recall him doing any testing.

Controller unit has not been fixed to the wall as I preferred to keep it portable.

Do you have a frost stat?

It's a Vokera Linea 28 combi boiler - as far as I'm aware it has a built in frost stat.

What happens if you carry the controller into the garage?

Exactly the same happened - relay box still showed no green led.

When I stood right next to boiler and switched off controller and then back on the green led came on and boiler fired up.

 

[D_Hailsham]

It's getting power from the same switched socket that powers the boiler.

Is it wired directly to the socket or via a junction box, or something else?

What happens if you press the button on the relay box (it should turn the boiler on and off)?

When I stood right next to boiler and switched off controller and then back on the green led came on and boiler fired up.

Check communication between controller and relay. Instructions are in the Installation Manual.

 

[jem16]

It's getting power from the same switched socket that powers the boiler.

Is it wired directly to the socket or via a junction box, or something else?

Directly to socket.

What happens if you press the button on the relay box (it should turn the boiler on and off)?

It turns the boiler on and off.

Check communication between controller and relay. Instructions are in the Installation Manual.

I tried the Test Communication - green led flashed every 6 seconds as described. I put it back to Auto and although flame was on again no green led on relay box.

I will try varying the position of the controller in case it's picking up interference from somewhere. Just strange it didn't do it yesterday.

Having read the installation instructions relay box is only around 15cns from boiler as opposed to 30cms - will this make a difference?