I have a new combi boiler with a Boss remote control thermostat. The comfort setting is at 18 degrees and the setback temperature is about 19 degrees (I don't really know what they mean and my gas engineer said he didn't!). However, on a morning I would like the temperature to be about 21 degrees, so even on auto my heating does not come on - I have to get out of bed early and tweak up the temperature to activate the boiler. When I increase the heating setting (comfort and setback) this seems to override the auto setting and the heating comes on randomly when we don't require it! Help please?

do what you want but look at manual for calibrating or troubleshooting stat

Comfort means a setting where you set it in the comfort zone. That's where you feel comfortable all the time.
Setback is the setting where you set it for a cooler temperature such as cooler setting when you go to bed.
Standby is a setting you have if either calling for heat or coolness. Standby is just waiting to come on either way.

because you have the temperature set at 28 degrees celcuis . Change the temperature to 18 degrees and it will cool 28 is hotter
It is a reverse cycle air conditioner it will warm the room if you set temperature to 28 degrees . Set it lower and it will blow out cold air.
Have exact same air conditioner as I recognise the remote control.
point it at the air conditioner when altering the temperature setting.
Check under the slide compartment also on the remote for more advanced settings.

Replace the thermosts,signal not getting thro to boiler.

It sounds like your heating system has to little capacity to heat the home properly. 21 degrees is a reasonable temperature to expect but if the unit is running all the time and can't reach 21 degrees the heater is too small.
As far as setting the thermostat here is a link to the instructions.
http://www.salus-controls.pl/data/product/attach/rt300rf_-_eng.pdf

A thermostat only cuts the heating off when the temperature it is set to is reached while the heating is on. If the heating is set to off then the thermostat will do nothing.
Generally you want to think about when you want your heating to come one and off by using the timer and then the thermostat is just used to ensure that you don't waste energy by exceeding the maximum comfortable temperature.

Hope this helps a little.

Setting a thermostat has nothing to do with outdoor temperature, but more to do with what is a comfortable setting for you and your utility bill.

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.

Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher. Furnaces put out the same amount of heat no matter how high the thermostat is set; the variable is how long it must stay on to reach the set temperature.

In the winter, significant savings can be obtained by manually or automatically reducing your thermostat's temperature setting for as little as four hours per day. These savings can be attributed to a building's heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures. For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial. By turning your thermostat back 10 to 15 degrees for 8 hours, you can save about 5 to 15 percent a year on your heating bill -- a savings of as much as 1 percent for each degree if the setback period is eight hours long.
Hope this helps..........

The reason I asked was to see if it is a power supply problem. If the setback had been set on 86 I would suspect you were having power fluctuations causing the heater to go the setback temperature. I will give this some more thought and post something else soon.

Just mark the old wires on the old thermnostat...R , W etc...and put them on the same terminals on the new 1.....also there should be some adjustment ire : switch on the back or under the cover to adjust for Hot water heating or electric heat...either is the setting you should have it on....also you shouldn't setback the thermostat at night or when away very much....2 degrees is fine , as the boiler will run along time to raise the temperature in the morning and may not get there by the set time

Here's the deal: If your Vitodens 100 has outdoor temperature sensing capability, either built in or via external aftermarket control such as Tekmar or other, and the temperature outside is above warm weather shut down (WWSD), then the boiler will not operate for space heating, but will operate to make Domestic Hot Water (DHW) only. Generally speaking WWSD is facoty set at 20*C, since this is normal room temperature so the boiler will not need to operate at temperatures above this number as it is warm enough outdoors to heat the house to comfortable levels.
If your Vitodens 100 does not have outdoor temperature sensing capability then you should check to see if your room thermostats are operational and calling for heat since the boiler is only responding to this on-off control based on room temperature. (turn up your room thermostats)
In both cases you need to make sure that your heating system's distribution pump and zone valves are operating correctly.
In any case you should be calling a heating contractor if you suspect that there is a problem with your boiler and/or heating system.
Good luck.