Servo drive for underfloor heating collector


Among the numer­ous equip­ment that is involved in the oper­a­tion of under­floor heat­ing sys­tems, you can find a small device that plays a cru­cial role in con­trol­ling and adjust­ing the heat­ing sys­tem. This is a ser­vo dri­ve, an electro­mechan­i­cal device, with­out which auto­mat­ic tem­per­a­ture con­trol for a warm water floor is not pos­si­ble.

The device is based on an elec­trother­mal reac­tion to a change in the heat­ing tem­per­a­ture of the coolant in the main sup­ply pipe and the sub­se­quent mechan­i­cal action, which, in com­bi­na­tion, ensures the open­ing or clos­ing of the flow of hot water into the heat­ing cir­cuits. Ser­vo dri­ves or ser­vo­mo­tors, offi­cial­ly in the lan­guage of pro­fes­sion­als, the device is called an elec­trother­mal ser­vo dri­ve, today they are present in almost all autonomous heat­ing sys­tems. New sub­ur­ban res­i­den­tial build­ings, cot­tages and dachas equipped with under­floor heat­ing are equipped with under­floor heat­ing, which is con­trolled by ser­vo dri­ves. It is the ser­vo dri­ve that is installed on the col­lec­tor for the under­floor heat­ing that per­forms the task of adjust­ing the flow of the coolant in the water floor heat­ing sys­tem.

Existing types of servo drives today

Among the cur­rent­ly exist­ing reg­u­la­tors that have become wide­spread in every­day life, there are the fol­low­ing ser­vo dri­ves. All devices can be divid­ed into sev­er­al types. Each vari­ety dif­fers in the prin­ci­ple of oper­a­tion and func­tion­al­i­ty. Accord­ing to the type of device design, there are two types:

  • closed;
  • open.

By the names you can judge the prin­ci­ple of action. Enclosed ser­vos are char­ac­ter­ized by an open posi­tion in the absence of pow­er. The incom­ing sig­nal acti­vates the mechan­i­cal part, block­ing the access of water to the sys­tem. For open type devices, the prin­ci­ple of oper­a­tion is reversed. In the nor­mal state, the ser­vo­mo­tor is closed, only when a sig­nal is received, the mechan­i­cal part is acti­vat­ed, open­ing the flow of water into the pipeline. You can judge which type is best for domes­tic use by eval­u­at­ing the capa­bil­i­ties of your own heat­ing sys­tem and the cli­mat­ic con­di­tions out­side the win­dow. Nor­mal­ly open ser­vo dri­ves are most often used in our coun­try.

On a note: if the device fails, the coolant in the pipeline con­tin­ues to cir­cu­late, leav­ing the floor warm for a cer­tain time. This fea­ture is espe­cial­ly rel­e­vant for coun­try hous­es locat­ed in a cold cli­mate zone.


Accord­ing to the method of pow­er sup­ply, ser­vo­mo­tors are divid­ed into devices pow­ered by a con­stant cur­rent of 24V and devices con­nect­ed to a con­ven­tion­al 220V AC pow­er sup­ply. Ser­vo dri­ves pow­ered by 24V are equipped with invert­ers.

Often, con­sumers use anoth­er, rather rare type of device. We are talk­ing about devices that are set to the nor­mal posi­tion depend­ing on the tech­no­log­i­cal require­ments of the heat­ing sys­tem. Such ser­vos are called uni­ver­sal and can change func­tion­al­i­ty from a nor­mal­ly open state to a nor­mal­ly closed state, and vice ver­sa.

All three types of ser­vo­mo­tors can be con­nect­ed to the col­lec­tor. The only con­di­tion is the cor­rect set­ting, bal­anc­ing and oper­at­ing con­di­tions of the heat­ing sys­tem.

Criteria for choosing the type of servo drive

In this sec­tion, we will try to answer the ques­tion. What is the basis for the choice of devices of one kind or anoth­er.

If you decide to equip your “warm water floor” heat­ing sys­tem with ser­vo dri­ves, con­sid­er the oper­at­ing para­me­ters of your heat­ing. In what posi­tion should the valve be most of the time. In a sit­u­a­tion where under­floor heat­ing is the main option for heat­ing res­i­den­tial premis­es for you, when hot coolant con­stant­ly enters the pipeline, rely on a nor­mal­ly open ser­vo­mo­tor. This view is ide­al for a long heat­ing sea­son.

On a note: in case of inter­rup­tions in the elec­tri­cal sup­ply, the fail­ure of the device will not stop the cir­cu­la­tion of warm water in the heat­ing water cir­cuits. The warm floor will con­tin­ue to be sup­plied with pre­pared water as a coolant.


For regions with a warm cli­mate, a nor­mal closed ser­vo­mo­tor is suit­able. If you are not afraid of defrost­ing the heat­ing cir­cuit, and you peri­od­i­cal­ly turn on floor heat­ing, this device will cope with its func­tions quite well.

Impor­tant! The ser­vo dri­ve for under­floor heat­ing with smooth adjust­ment has an elec­tron­ic type reg­u­la­tor. Such devices more accu­rate­ly respond to changes in the tem­per­a­ture of the coolant flow, smooth­ly mov­ing the stem to the desired posi­tion. Con­tin­u­ous­ly adjustable ser­vo­mo­tors are designed for under­floor heat­ing, in which it is often nec­es­sary to dose the vol­ume of the incom­ing flow.

In most cas­es, such devices are not used in home heat­ing sys­tems with under­floor heat­ing. There­fore, when buy­ing, pay atten­tion to whether or not the instal­la­tion of an elec­tron­ic reg­u­la­tor is required for the device. If the instruc­tions say that such equip­ment is nec­es­sary, then you are deal­ing with an elec­tron­ic ser­vo. Let’s say right away that it is inex­pe­di­ent and unprof­itable to use such a device at home.

Be sure to read: how to make a water floor from a gas boil­er?

The device and principle of operation of servomotors

The main work­ing ele­ment of the ser­vo dri­ve is the bel­lows. Those. the same part as in the three-way valve. Small in size, her­met­ic cylin­der with an elas­tic body is filled with a sub­stance that is sen­si­tive to tem­per­a­ture. Depend­ing on whether there is an increase or decrease in tem­per­a­ture, there is a cor­re­spond­ing change in the vol­ume of the sub­stance. Fig­ure — the dia­gram clear­ly demon­strates the device of the ser­vo­mo­tor, where the main place is occu­pied by the bel­lows.

The bel­lows is in close con­tact with the elec­tri­cal heat­ing ele­ment. Receiv­ing a sig­nal from the ther­mo­stat, the heat­ing ele­ment is switched on from the net­work and put into oper­a­tion. Inside the bel­lows, the sub­stance is heat­ed and increas­es in vol­ume. Thus, the enlarged cylin­der begins to put pres­sure on the rod, chang­ing its posi­tion and block­ing the path to the coolant flow. Eval­u­at­ing the oper­a­tion of the ser­vo dri­ve, we can con­clude that the device is not equipped with any motors, it does not have any gears and trans­mis­sion links. The usu­al work­ing rela­tion­ship is “ther­mal ener­gy and elec­tric­i­ty”. Hence the com­mon name of the devices, ther­mo­elec­tric con­trollers.

In order for the valve to become open again, the whole process is repeat­ed only in the oppo­site direc­tion. Lack of pow­er caus­es the heat­ing ele­ment to stop work­ing. Con­se­quent­ly, the sub­stance inside the cylin­der cools down, decreas­ing in vol­ume. The pres­sure on the stem decreas­es, it ris­es, act­ing on the valve, and, con­se­quent­ly, access of hot water to the sys­tem opens.

On a note: the sub­stance placed inside the cylin­der is toluene, which has high ther­mo­dy­nam­ic char­ac­ter­is­tics. Nichrome fil­a­ment acts as an elec­tric heat­ing ele­ment.

Hav­ing become acquaint­ed with the prin­ci­ple of oper­a­tion of the device, it is impor­tant to remem­ber that a cer­tain time is required for the mechan­i­cal action of the valve. Despite the fact that when a sig­nal is received from the ther­mo­stat, the heat­ing ele­ment begins to heat the sub­stance inside the cylin­der. The time required for changes in the phys­i­cal state of the liq­uid is 2–3 min­utes, so the valve is not actu­at­ed imme­di­ate­ly.

For ref­er­ence: when choos­ing a ser­vo dri­ve mod­el, pay atten­tion to the para­me­ters of the heat­ing ele­ment and the liq­uid heat­ing time indi­cat­ed in the device pass­port.


Unlike heat­ing, the cool­ing of the liq­uid is slow­er. For the reverse process, i.e. it will take not 2–3 min­utes to close the valve, but 10–15 min­utes. When over­heat­ed, each ser­vo­mo­tor should auto­mat­i­cal­ly shut down. To do this, the design pro­vides an emer­gency shut­down mech­a­nism.

For exam­ple: not all ser­vo dri­ves used in the work of the col­lec­tor group are equipped with cylin­ders and cylin­ders with a sub­stance. There are mod­els in which ther­moele­ments play this role, resem­bling a spring or a plate, which are heat­ed under the action of the same heat­ing ele­ment. Expand­ing, these parts again act on the stem, ulti­mate­ly bring­ing the valve into work­ing con­di­tion. You can deter­mine in what posi­tion the valve is locat­ed by chang­ing the appear­ance of the ser­vo. The retractable ele­ment indi­cates the oper­a­tion of the device. If this does not hap­pen, then your appli­ance is not con­nect­ed cor­rect­ly or the heat­ing sys­tem is inter­mit­tent.

For ref­er­ence: a ser­vo motor that is hot to the touch means that in this case the device is closed and switched off. If the device is cool to the touch, there­fore, the valve is open, the coolant cir­cu­lates nor­mal­ly through the water cir­cuits of the warm floor.

Servo drive installation. Features and nuances

Before installing the ser­vo dri­ve, decide what type of ther­mo­stat the device will have to inter­act with. In cas­es where the ther­mo­stat con­trols the oper­a­tion of one water cir­cuit, both devices are direct­ly con­nect­ed by wires. When it comes to using a mul­ti-zone ther­mo­stat, a device that serves sev­er­al pipelines at once, the con­nec­tion of ser­vo­mo­tors is car­ried out as fol­lows.


In order to prop­er­ly con­nect all the wires and ter­mi­nals, a floor heat­ing switch is used. The func­tion of this device is to con­nect and con­nect devices for var­i­ous pur­pos­es into a sin­gle cir­cuit. In addi­tion to the dis­tri­b­u­tion and link­ing func­tion, the switch also plays the role of a fuse. In sit­u­a­tions where all shut-off valves of the water cir­cuits are closed, the switch turns off the pow­er to the cir­cu­la­tion pump.

The switch is very con­ve­nient in cas­es where under­floor heat­ing is pow­ered by an auto­mat­ed autonomous gas boil­er. The fig­ure shows how ther­mostats and ser­vo­mo­tors are con­nect­ed to a sin­gle con­trol sys­tem.

Actuator installation location, manifold mounted thermostatic valve.

Impor­tant! When the heat­ing sys­tem is oper­at­ing, under­floor heat­ing from a sol­id fuel boil­er, such a switch func­tion as turn­ing off the pump is fraught with stop­ping the heat­ing device itself. Installing a bypass and bypass valve will allow you to avoid stop­ping the pump and run­ning the heater at idle.


It should be not­ed that thanks to the emer­gence of mod­ern devices and devices, the man­age­ment and adjust­ment of under­floor heat­ing has become an ordi­nary and sim­ple process. The design of many devices used for the oper­a­tion of heat­ing cir­cuits is not par­tic­u­lar­ly dif­fi­cult. The prin­ci­ple of oper­a­tion of many com­po­nents and assem­blies is also clear. This can be said with cer­tain­ty about ser­vos. The devices are most­ly reli­able, prac­ti­cal and easy to use. Thanks to ser­vo­mo­tors, it became pos­si­ble to ful­ly auto­mate the con­trol sys­tem for under­floor heat­ing, to make the con­di­tions for using heat­ing equip­ment sim­ple and under­stand­able.

Choos­ing a sim­pler option, you can get by with the instal­la­tion of con­ven­tion­al con­trol valves. Auto­mat­ic reg­u­la­tors, ther­mal sen­sors and ser­vo dri­ves, a cat­e­go­ry of devices that work for your com­fort and safe­ty. Installing addi­tion­al devices, such as a switch and a bypass valve, will make your heat­ing sys­tem as effi­cient and safe as pos­si­ble.


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