Charmeg MP-A Installer Manual

The directions given on this sheet concern the following products: 

•  MR-R 

•  MP-A 

•  MP-SW 

•  MP-N 

•  MP-F 

•  MP-T 

•  MP-TM 

In all the above products apart of the temperature set-point which is explained in the respective User’s Manuals, some 

additional operational parameters can be modified. 

A. the Differential  

B. the Offset 

C. the Upper and Lower Adjusting Limits 

D. the Maximum Allowed Floor Temperature (only for MP-F) 

The meaning of each of them  as well as  the step by step process of modifying those parameters is explained below. 

ATTENTION 

The modifications must be performed always from experienced and officially registered personnel. No end user 

should try to perform this modification. The necessity of parameter change from a pre stored value as well as the 

consequences to the system are fall in to the exclusive liability of the installer engineer.  Charmeg has no liability for 

possible damage might be induced as a result of inappropriate or wrong parameter modification.  Do not hesitate to 

consult Charmeg in case of any misunderstanding.  

Parameter Content  

Differential is the minimum detected temperature change that is necessary for a thermostat in order to toggle its output 

state. Consider for example a room thermostat adjusted at 20°C. Assume the environmental temperature at 15°C. The 

thermostat tries to maintain the desired temperature as perfect as it can. When the room temperature reach the predefined 

20°C set point the thermostat deactivates the heating system. The room temperature normally overshoots slightly above the 

20°C and then decreases rapidly. The set point value minus the temperature point in which the thermostat will activate again 

the heating system defines the differential. Because the desired temperature is higher than the heating demand temperature 

we trend to say that the differential considered negative. In such a case the room thermostat could have a differential of –

0.6°C. Consequently the room temperature should drop 0.6°C below the 20°C in order to allow the thermostat to reactivate the 

heating system. The system will be activated again at 19.4°C. The smaller the operating differential the more precise the 

temperature control.  In the above example the closest to 20°C the room temperature will be. Indeed in reality some additional 

factors interfere the control process and the absolute control remains unreachable. Moreover the small differential can cause 

more frequent cycles to the burner of the heating system resulting huge wear out. Tiny differentials should be avoided. In 

practice values from –0.6°C to -0.8°C have good results in home and office installations. 

Offset is the parameter that adds or subtracts a constant value from the temperature read by the thermostat in order the 

final temperature to be closer to the real one. If for example the thermostat displays wrongly 17.5°C while the correct is 18°C 

we can rationally conclude that there is an error of -0.5°C. The offset parameter adds this missed 0.5°C to the measurement. 

The result is a corrected and accurate temperature reading. Exactly the opposite should be done in case of bigger measured 

temperature. If the thermostat displays 18.8°C an offset of  0.8°C should be subtracted from the reading. Generally speaking 

the offset value is applied to eliminate the small measuring constant errors they can be present in massive production devices. 

Another useful case is when the thermostat has been wrongly installed near to any source (lights, heat radiator) or sink 

(window, openings etc) of heat and due to the influence of the source shows incorrect reading.  In those cases offset capability 

gains crucial importance.  

You should be aware of the offset modification. Any possible change must be done carefully. It is considered ineffectual trying 

to extinguish differences as low as +/-0.5°C. Particularly room thermostats are not measuring instruments. They include 

temperature displays in order to inform the inhabitants for the present room air temperature with a limited degree of accuracy. 

Because of the tolerances of the used electronic devices, the inappropriate places of installation as well as other reasons 

render thermostat to be susceptible to various parameters which affects accuracy. If somebody would try to comprise a 

perfectly measuring device will not unlikely result to double its cost. The most important is to have an indication of the 

temperature and gather the information regarding the degree of comfort. If the inhabitants feel good when the thermostat 

shows 20°C it is worthless to reveal that the real temperature is slightly above or below 20°C. The modification of the offset 

must be performed for the temperature point in which thermostat is to be operated most of the time. For a heating room 

thermostat this point is about 22°C. If the working point in unknown use the middle of the adjusting range. For the MP-R this is 

(35°C-5°C)/2+5=20°C. 

Digital Thermostats MP Series 

Installer’s Manual

Upper and Lower Adjusting Limits The members of MP series are able to control the temperature among the limits 

described in those manuals. It is although very common a tightest adjusting range to be necessary in order to protect the 

premises or even the users. For example in thermostats installed in the rooms of a hotel a narrower range might be more 

preferable.   

Maximum Allowed Floor Temperature (only for MP-F) In under floor designated thermostats an additional feature is 

unexceptional. The device measures also the floor temperature and takes track to be always under a predefined limit (usually 

45°C). If the temperature exceeds this limit the thermostat interrupts the heat demand signal protecting the overall under floor 

piping from overheating. The floor maximum temperature can be trimmed in MP-F.  

Parameter Modification 

In the following table directions for the necessary actions in case of parameter modification can be found. Inside the 

parentheses are the factory pre stored values.  

Desired T emperature 20

°C  

Time t 

R

oom

 T

em

perat

ure

 Τ

Maximum T emperature Τ max 

Minimum T emperature Τmin 

Differential 

ΟΝ 

ΟΝ 

ΟΝ 

Burner 

27 Kotronos str. Aegaleo- Athens- Greece  

Tel.+30 210 5693111 Fax +30 210 5693093, www.charmeg.gr 

Doc. No: Installers_manual_MP_gr_en_3.doc