Programmable Thermostat and Boiler Programmer

[Ed932]

I have a Honeywell 7 day programmer (controls water and heating independently) and has 3 on off periods.

The installer installed this with a Drayton wireless room stat.

It was suggested to me that I upgrade this to a programmable stat so I have a Drayton 7 day programmable thermostat now (uses the same receiver).

I programmed the stat to the on/off periods and temperatures required. Generally the winter so far has been mild such that the reading on the stat has been at the level programmed. Therefore I would expect the heating to be off.

However it seems to be on at times I would not expect, particularly at night time.

I have left the honeywell boiler prog at the same on/off settings as before as assumed the stat would over-ride this if required?

I did have the programmer on constant but this seemed worse.

How should I have this set up?

Regards

Ed

 

[D_Hailsham]

The Honeywell programmer should be set to continuous for CH so all control is done by the Drayton prog stat.


What times and temperatures have you set?

 

[Ed932]

I thought it should be on constant but turned it off as CH was coming on at night.

The stat is programmed on a 5+2 day schedule.

5 days/week -

5:40 - 9 am - 20 deg
9 am to 12 noon - 18 deg
12-2pm - 20 deg
2 - 4pm - 18 deg
4 pm - 10 - 20 deg
10pm to 5:40 - 12.5 deg

Stat is in hall and when stat shows at 20 deg house is comfortable temp. Should we have shorter time frames or bigger temp variations?

The above is a variation on a preprog profile that came on stat but I lowered the temp slightly on each setting

Ed

 

[D_Hailsham]

The time/temperature schedule looks OK, although I doubt if you will save anything by dropping the temperature from 20C to 18C.

If the boiler is coming on in the night, it suggests that the house is cooling down fairly quickly to below 12.5C. You can easily check this by setting the overnight temperature to 5C.

How well is the house insulated?

 

[Ed932]

Thanks for coming back. I guess I had assumed the house wouldn't drop below that level but maybe it is.

I'll test the 5 degree idea and see what happens.

It is a 1950's solid brick detached house. Double glazed (oldish units) but has got reasonable loft insulation as have increased that significantly which made a huge difference.

Regards

Ed

 

[D_Hailsham]

It is a 1950's solid brick detached house.

I would be very surprised if it was solid brick. Cavity walls were standard then.

 

[Ed932]

Now confused, something controlling boiler but not sure what.

Like your recommendation I thought constant best plan. Reduced overnight temp to get boiler to cut off. Middlem of night and heating on and display on stat reads 19 so boiler should be off.

Put programmer to be off overnight and despite this and temp on stat reading higher than requirement heating on.

Did some tests on stat and putting temp up flames displays and receiver show relevant signal. As I write this earlier temp dropped so stat kicked in and flame signal. Now stat reads 21 no flame symbol so boiler should be off but on.

Boiler has first stat as well as in garage but last few nights mild so don't see this as issue.

Any ideas on how to resolve or isolate what the rogue component is?

Ed

 

[D_Hailsham]

Boiler has first stat as well as in garage but last few nights mild so don't see this as issue.

Do you mean a frost stat?

What temperature is it set to?
Is there also a pipe stat connected in series with the frost stat?

 

[Ed932]

There is Honeywell frost stat which is size of a light switch plus a pipe stat as well. Pipe stat has dial on it which goes from 0 to 40. Never touched it before but tweaking it down from the 20 it was on to about 15 the boiler went off ( as i write this).

Given boiler is towards front of garage what ought it be set at?

Ed

 

[D_Hailsham]

20C is normal for the pipe stat. (The boiler will turn off when the water temperature reaches this.)

What is the frost stat setting? (The boiler will come on when the air temperature drops to this), If the frost stat is set too high the boiler will come on unnecessarily. A temp of 5-7C should be OK.

 

[Ed932]

How do you set the frost stat as looks like a plain sealed box?

Ed

 

[D_Hailsham]

How do you set the frost stat as looks like a plain sealed box?

The frost stat has a tamper-proof cover, which can be removed. Turn power off while doing this.

 

[Ed932]

Yes see that is set to 5 degrees. So,frost stat turns it on and pipe turns it off?

Tweaking the pipe stat down slightly seemed to turn heating off perhaps it is set to too high a min whilst frost stat at 5 degree is sensible min?

Ed

 

[D_Hailsham]

The frost stat turns the boiler ON when the temperature drops to 5C. If the pipe stat wasn't there, the boiler would run continuously all the time the frost stat showed 5C or lower. The water would get hotter and hotter until the boiler thermostat turned the boiler off - at about 75C. This is unnecessary and wastes gas.

The pipe stat turns the boiler off when the water temperature has risen to the set value (15C to 20C). This means the water never freezes and never gets too hot.

It sounds as if your garage gets colder than you realize.

PS The pipe stat should be on the return from the heating system.