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Temperature thermostat not working as you expect? Discover why


Temperature thermostats – even the most modern ones – are generally not difficult to use. Functionality and user-friendly menus are the first condition to make them useful. Accurate temperature control is the second, but today we will focus on the problems we may encounter in the implementation and subsequent use of these devices. Why the temperature thermostat doesn’t work?

It sometimes happens that temperature thermostats stop working or, if we are at the installation stage, do not start working. To save time and nerves, it is worth looking at the reasons that may have disturbed their operation before starting the complaints procedure. Some problems require service repair, but with most we can deal ourselves.


If the thermostat has been working properly for some time and suddenly stops, the first thing to do is to replace the batteries and check whether the problem still appears. This is because it can happen even though there is no indication that they need to be replaced, the power supply becomes weaker and the device starts playing tricks on the user.

In the case of SALUS Controls temperature thermostats, a set of batteries is enough for about two heating seasons. However, if you notice any errors earlier; unplanned start-ups of the heat source, inaccuracy of the schedule, start with the batteries.

REMEMBER: Before sending the thermostat for service, make sure it has working batteries. Partially discharged batteries can weaken the signal.

Incorrect connection

The problem can appear when wired thermostat are installed.

It is always a good idea to follow the recommendations given in the wiring diagrams. It is not just a matter of routing the cables correctly, but also of their choice. The use of unsuitable cables will make it impossible to use all the functions of the device.

For example, if we are connecting SALUS Controls thermostats from the Expert series, it is recommended to use 4 x 0.75 mm² or 4 x 1 mm² cable. We will then use all the functions of the thermostats. If we use a three-core cable, we will not have access to the night temperature reduction function (NSB; Night Set Back).

It is also worth remembering that the wiring insulation should be suitable for a 230 V system.

What is important, „twisted-pair” Internet cable, despite the required number of wires, is not a good choice for a 230 V system because of the cross-section of the wires and the class of insulation. However, if the installer installed such wires we can choose a 24 V system.

Temperature thermostat does not work due to lack of communication with the receiver

The problem may appear when installing older type of wireless thermostat.

If the transmitter does not communicate with the receiver, make sure that the communication code of the transmitter and the receiver is set correctly. If the receiver controls the boiler not according to the transmitter’s indication, you need to change the communication code to a different one than factory.

To avoid this mistake, it is worth getting newer controllers. For example, the bestselling thermostat for boilers and other heat sources by SALUS Controls – 091FLRFV2 – does not require manual setting of codes. It contains as many as 64,000 combinations, so that a situation in which our thermostat is „activated” by an unauthorized device is practically impossible.

And even if – by extreme bad luck – this will happen, all you have to do is re-pair the transmitter with the receiver (for your convenience, the outputs are factory paired).

The temperature thermostat does not work because the devices have lost communication with each other

This problem can appear with a system that works wirelessly in a home network. It happens that the temperature thermostat stopped heating the room properly because it lost communication with the wiring centre or with the TRV head. At that point, it is useful to re-pair devices and even reinstall your control automation. It has been known for a long time that a reset allows electronics to take a „new breath.”

When 091FLRFV2 loses connectivity, we also re-pair the thermostat.

The thermostat turns on the boiler instead of turning it off, and vice versa

Most SALUS Controls thermostats are equipped with COM/NO (normally opened) contacts for connecting the boiler, which turns on the heating by shorting circuit contact. However, if the automation of our boiler turns on the heating by opening them, a thermostats with COM/NC (normally closed) contacts will be required.

In the 091FLV2 and 091FLRFV2 thermostats, you can change the relay type programmatically and everything will work as it should. So, in order to avoid complications, let’s look for controllers that are as universal as possible.

Wrong thermostat placement

We often do not pay attention to where we mount the control device. We follow either interior design, decorations or… random choice. Meanwhile, the room thermostat should be installed in the right place – non-sunny, far from drafts, fans, radiators, fireplace, stove, or even a lamp. It is good to hang/set it at a height of about 150 cm.

This is important because a bad location can cause the temperature sensor built into the unit to false readings, causing the room to be underheated (most often). If the temperature on the thermostat is falsely high, the boiler will not turn on, and the room will be cooled. So when choosing a place for the controller, it is worth taking into account not only convenience. Avoid places that expose the thermostat to large thermal fluctuations. If we forget about this, we are very likely to consider that the temperature thermostat is not working properly.

In the case of wireless thermostats, undisturbed communication between the transmitter and the receiver is also extremely important. It is necessary to take into account not only the distance between the devices, but also possible architectural obstacles (such as walls) that may cause the signal not to reach the receiver.

Mistakes in setting the schedule or selecting the control algorithm

Although programming the schedule should not be complicated, mistakes can happen. If our temperature thermostat doesn’t work properly – it doesn’t send the heating demand, even though according to our expectations it should, the reason could be, for example, setting the night temperature reduction at the wrong time period.

The choice of the wrong control algorithm for our type of heating system, such as hysteresis for underfloor heating, can also be a problem. Hysteresis operation is based on slight overdrives, so it does not guarantee precision. Underfloor heating, on the other hand, has a long response time, high thermal inertia, so the heating effect may not be satisfying.

Before we consider that the controller starts at the wrong time or does not start at the indicated times or parameters, we will check the temperature ranges we have entered for each time of day and night.

We will also adapt the control algorithm to our type of installation. SALUS Controls mostly offer two control algorithms to choose from – hysteresis and TPI. By choosing hysteresis, you can specify its range. Deciding on the TPI algorithm, you can indicate what type of heating it is to be used for (floor, radiator or electric).

Devices designed specifically for underfloor heating also operate based on the PWM algorithm. This function allows the inertia of the underfloor heating, so it closes/opens the actuators appropriately earlier/ later, preventing the room from overheating or cooling down.

Temperature thermostat does not work properly by incorrect control

Finally, remember that we should always adjust the parameters of room thermostats to suit our lifestyle. To do this, you should carefully read the instruction manual, ask the installer or manufacturer of the control automation you purchased.

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