Boiler control with or without a pump – what is the difference and what do I need
Boiler control with or without a pump – what is the difference and what you really need
When a customer comes into the store or contacts us online with the question "I want a boiler controller, but I don't know if I have a pump or not" – this is a question that comes up literally every week. And it's no wonder. The vocabulary around heating technology is full of terms that are unclear to laypeople, and controller manufacturers make the situation worse by each calling the same thing slightly differently. That's why this article doesn't start with controllers, but with the system itself – how heat travels from the boiler to the radiators, and what that has to do with choosing the right controller.
Here you'll find technical explanations, specific examples from our order practice, wiring diagrams, and answers to the most frequently asked questions. If you just want a quick answer to "what should I buy" – skip to the conclusion. If you want to truly understand the topic, read the whole article. It's worth it for any controller you'll use for years to come.
How the heating circuit works – the basics without which nothing will fit together
Every boiler – gas, oil, solid fuel, heat pump – has the task of heating water. This water must somehow travel from the boiler to the radiators (or to the underfloor heating) and back. There are two principles for this:
1. Gravity (thermosiphon) circulation – water circulates by itself due to the difference in density between hot and cold water. Hot water rises, cold water sinks. This principle was used in old, traditional boiler rooms with large-diameter pipes and radiators positioned higher than the boiler. Today we only encounter it in old family houses where the installation hasn't been rebuilt.
2. Forced circulation with a circulation pump – the circulation pump (colloquially "pump") pushes water through the system independently of physical laws. Modern houses, new builds, renovations – all work with forced circulation. The pump is either part of the boiler (a so-called compact condensing boiler, wall-mounted boiler) or is located externally in the boiler room on the pipe.
Why is this important for choosing a controller? Because the boiler room control needs to know what it has to control. If your system has a circulation pump (for example, a standalone pump in the boiler room, or a pump built directly into the boiler), the controller must reflect that – either it starts and stops the pump itself, or it works together with it via other signals. If you don't have a pump (gravity system), the control logic is completely different.
Control without a pump – when and for whom
In practice, we encounter gravity circulation mainly in houses built before 1990, where the heating hasn't been renovated. Typical signs: thick cast-iron pipes with a diameter of 3/4" to 1", heavy cast-iron radiators, boiler located at the lowest point of the system. In such houses, there simply is no circulation pump, or one was installed later as a backup.
The controller for such a system only controls the boiler – i.e. the burner assembly or electric heating. It switches the boiler on and off according to the room temperature or a set program. You don't control a pump, because there isn't one. In practice, this means a simpler electrical scheme – the controller only needs one output circuit (for the boiler), not two (boiler + pump).
However, be careful: even in houses with gravity circulation, a small circulation pump is increasingly being installed today to improve heat distribution and shorten warm-up time. In that case, it's a mixed system, and the controller should also be able to control this pump.
Control with a pump – the standard for modern boiler rooms
Most boiler rooms we encounter today, whether in renovations or new builds, include a separate circulation pump. The pump can be:
- Integrated into a condensing boiler – wall-mounted gas boilers (e.g. Vaillant, Viessmann, Buderus) have the pump built in directly. In this case, the controller communicates with the boiler via OpenTherm or a simple switching contact, and the boiler usually controls the pump itself.
- External circulation pump on the pipe – standing solid fuel boilers, oil boilers, older gas boilers, air-to-water heat pumps with external hydraulics. Here the pump isn't controlled by the boiler, but by the boiler room controller.
- Multiple pumps – multi-circuit systems with underfloor heating, a DHW tank, a solar circuit. Each circuit has its own pump, and advanced controllers control each one separately.
So a controller "with a pump" means it has at least one output relay circuit designed to start and stop the pump. This is a fundamental technical difference compared to a simple room thermostat, which doesn't have such an output.
What exactly does a boiler room controller do and why isn't a room thermostat enough
This is one of the most important questions we need to explain to customers. A room thermostat – the simple one you might have had on the wall since the 90s – has the task of switching the boiler on and off according to the air temperature in the room. It has one output: a relay contact that closes when it's cold and opens when it's warm enough. Nothing more.
A boiler room controller does much more:
- Controls the boiler and pump separately – it can turn off the boiler but leave the pump running (important for cooling the boiler after shutdown, or for burn-out in solid fuel boilers).
- Contains frost protection – when the temperature drops below a set value (usually +3 to +5 °C), it automatically starts the boiler and the pump.
- Implements weather-compensated (equithermal) control – based on the outdoor temperature (measured by an outdoor sensor), it sets the outlet water temperature, not just switches the boiler on/off. Result: the boiler doesn't run in "full power – off" cycles, but modulates smoothly. You can find more on this topic in the article Weather-compensated control – how it works and when it's worth it.
- Allows setting a daily and weekly program – lowering the temperature at night or during working hours.
- Protects the boiler and the system from condensation on the heat exchanger in old non-condensing boilers – the return temperature must not fall below approximately 50–55 °C.
- Allows DHW heating priority – if you have a domestic hot water tank, the controller can temporarily interrupt the heating circuit and redirect energy to the tank.
A simple room thermostat can't do any of this. And that's exactly why a boiler room controller is an investment that pays off – not only in comfort, but also in fuel savings.
Adex – a typical representative of controllers for Slovak boiler rooms
In the Slovak market, ADEX controllers are among the most widespread and reliable products for controlling boiler rooms in family houses. They are manufactured in the Czech Republic, have a long history, and importantly – their documentation and technical support are available in Slovak and Czech, which is very helpful during installation and setup.
For a standard boiler room with one boiler and one circulation pump, the ideal solution is the Adex midi Controller. It's a compact controller with two output circuits (boiler + pump), an input for both room and outdoor sensors, and simple setup. It handles most common scenarios in a family house: a gas or oil boiler with an external pump, a solid fuel boiler with storage tanks, or an electric boiler with forced circulation.
For more demanding applications – multi-circuit systems, controlling multiple pumps, switching DHW vs. heating priority – there is the ADEX Comfort 6 Controller. It has six output circuits, which is enough even for more complex boiler rooms with underfloor heating, a DHW tank, and a solar circuit.
If you're dealing with a system where the boiler doesn't have its own sensor and you want a simple controller with a clamp-on thermostat on the pipe (e.g. for solid fuel boilers), a suitable addition is the ADEX TTUV Electric Thermostat, which works as a clamp-on thermostat directly on the boiler's outlet pipe.
Outdoor sensor – when I need it and when I don't
The outdoor sensor is a key element of weather-compensated control. It measures the outdoor air temperature, and the controller uses it to determine what the heating water temperature should be. The logic is simple: at -15 °C we need the water in the radiators to be hotter than at +5 °C.
Without an outdoor sensor, the controller only works in thermostatic switching mode – switching the boiler on and off according to the room temperature or a set value. This is sufficient for basic applications, but doesn't allow true weather-compensated control.
For outdoor temperature, for example, the ADEX B Outdoor Sensor is designed – a simple resistive NTC sensor that is connected to the controller by cable. It's mounted on the north or northwest wall of the building, away from sunlight and direct rain, at a height of at least 2–2.5 m above the ground. Correct sensor placement is essential – you can find more on this topic in the article Clamp-on pipe thermostat – how to correctly place and set the sensor.
Practical examples from the field – what actually occurs
Case 1: Old house, cast-iron radiators, natural gas boiler with simple automation
The customer had an older standing gas boiler (e.g. Protherm Medvěd) in the boiler room with simple integrated automation but no weather compensation. The pump was external, on the return pipe. On the wall hung an old mechanical thermostatic head used as a room thermostat. Problem: the boiler ran either at full power or not at all, the house overheated and then cooled down, and the gas bill was unnecessarily high.
Solution: Installation of a controller with an outdoor sensor (e.g. Adex Comfort R Controller), connecting the ADEX B outdoor sensor to the north wall, setting the weather compensation curve according to the building's characteristics. Result: the boiler works in much smaller power steps, the temperature in the house is more stable, and gas consumption dropped by about 12–18% (typical results with proper weather-compensation setup in old houses).
Case 2: New build, air-to-water heat pump, underfloor heating
The heat pump has its own internal control, but the customer wanted a central boiler room controller that would also coordinate the DHW tank, the underfloor heating circuit, and an additional electric backup heater. In this case, a multi-circuit controller is needed that can control each circuit separately. For such a scenario, the ADEX Comfort 6 Controller with six output circuits is suitable.
Case 3: Wood boiler + storage tank + radiator circuit
This is a typical scenario where mistakes are most often made. The customer wanted to control a wood boiler but didn't understand that with a solid fuel boiler, you can't simply "turn off" the boiler – once combustion has started, you can't stop it. Correct logic: the controller monitors the temperature in the storage tank (not in the room); when there is sufficient stored heat, it turns off the primary circuit pump (boiler → storage), and when the temperature in the tank drops, it starts the secondary circuit pump (storage → radiators). For this you need a controller with at least two outputs (two pumps) and two temperature inputs (boiler sensor + tank sensor). The ADEX TTUV clamp-on thermostat is used precisely for measuring the temperature in the tank or on the pipe.
Case 4: A cottage that is empty most of the year
The customer wanted a controller for a cottage with an electric boiler. Main requirement: frost protection during absence, but minimal electricity consumption. Ideal solution: a controller with adjustable frost protection (e.g. +5 °C) and a time program option – the system heats up to a comfortable temperature before arrival at the cottage. A simpler, cheaper controller model is fully sufficient here, since neither weather compensation nor multiple circuits are needed.
How to choose the right controller – a systematic approach
Before buying a controller, answer these questions:
1. What type of boiler do you have? Wall-mounted gas (with integrated pump), standing gas, oil, electric, solid fuel boiler, heat pump? This determines what outputs the controller needs.
2. How many circuits do you have? One radiator circuit, or also underfloor heating, a DHW tank, a solar circuit? Each circuit = one controller output (or an electric valve + pump).
3. Do you want weather compensation? If so, you need an outdoor sensor and a controller that supports the weather compensation curve. If not, thermostatic switching based on room temperature is enough.
4. How technically skilled are you for installation? Some controllers are simpler to wire, others require a qualified electrician. You can find more about installation in the article Installing a boiler room controller step by step – what you can do yourself and what needs an electrician.
5. Are you interested in remote control? Modern controllers allow Wi-Fi or GSM connection and control via a mobile phone. If you want this, you need to take it into account when choosing a model.
You can find a comprehensive view of choosing a controller in the article How to choose a boiler room controller – what to focus on before buying, where we cover the topic systematically from A to Z.
Technical parameters you need to understand before buying
When you look at a controller's data sheet, you'll come across these terms:
- Number of output circuits / relays – how many devices (pumps, boilers, valves) the controller can control separately. At least 2 for a single-circuit system with a pump.
- Relay output load capacity – given in amps (e.g. 5 A or 10 A at 230 V). Low-power circulation pumps (15–50 W) have no problem even with a 5 A relay, but you need to check the pump's starting (inrush) current, which can be 3–5 times higher than the rated current.
- Type of input sensor – NTC (resistance decreases with temperature, common standard), PT1000 (resistive, more precise, used by better controllers), thermocouple (only for very high temperatures, rare in ordinary boiler rooms).
- Temperature measurement range – important for solid fuel boilers, where the temperature can rise to 90–95 °C. The controller must be able to handle the entire range.
- Protection rating (IP) – controllers in a boiler room must have at least IP30 (protection against dust and accidental contact). If the boiler room is damp, require IP44.
- Communication protocol with the boiler – OpenTherm, eBus, ModBus. Some boilers require a specific protocol for power modulation (not just ON/OFF switching). Check compatibility.
The most common mistakes when choosing and wiring a controller
From dozens of orders we've dealt with, several recurring mistakes emerge:
The customer buys a controller without a pump output and is then surprised that the pump has to be controlled manually. This happens when a simple room thermostat is bought instead of a boiler room controller. Solution: always check how many output relay circuits the controller has.
Incorrectly placed outdoor sensor. A sensor on the south wall in direct sunlight = the controller thinks it's warmer outside than it actually is, and doesn't heat the boiler enough. Solution: north or northwest wall, shaded position.
A solid fuel boiler without a storage tank controlled like a gas boiler. The controller "turns off" the boiler (by interrupting the supply of the primary circuit), but the boiler keeps burning → overheating → safety valves open, the boiler gets damaged. This is a dangerous mistake that can lead to boiler failure.
Poorly chosen weather compensation curve. A steeply set curve → boiler running at high temperature even in relatively warm weather → unnecessary losses. A shallow curve → the house doesn't get warm enough during severe frosts. Setting it up requires several weeks of tuning during the heating season. You can find more about controller problems in the article Common boiler room controller faults – pump not running, sensor error, thermostat not responding.
Controller integration with the domestic hot water tank
If you have a DHW tank in your house (a boiler heated from the boiler), the controller should be able to handle so-called DHW priority. Principle: when the tank needs to heat water, the controller temporarily stops the heating circuit pump and redirects the boiler's entire output to the tank. Once the set DHW temperature is reached (usually 55–60 °C), heating resumes.
For households with higher DHW consumption (larger families, bathrooms), this mode is important – without it, the tank heats up slowly and comfort decreases. Controllers like the ADEX Comfort 6 fully support this mode.
What if my boiler has a built-in controller – is an additional external controller unnecessary?
This is a legitimate question, especially with modern condensing boilers that have their own sophisticated electronics. The answer depends on what you want to achieve:
If basic control using the boiler's electronics is enough for you (setting the water temperature, a simple room thermostat), an external controller isn't necessary. However, if you want weather compensation based on outdoor temperature, control of multiple circuits, a weekly program with multiple temperature levels, or integration with a DHW tank – an external controller or expanding the boiler's electronics with accessories makes sense.
For solid fuel boilers and old non-condensing boilers, an external controller is practically always necessary, because these boilers don't have their own advanced electronics.
Frequently Asked Questions (FAQ)
Can I use a room thermostat instead of a boiler room controller if I have an external pump?
Technically yes, but only if the boiler has its own automation board that controls the pump independently. If the pump doesn't have its own control (e.g. an older standing boiler), you must have a controller with a pump output. Otherwise the pump would run constantly (unnecessary consumption) or not at all (boiler overheating). You can find more about this distinction in the article Room thermostat vs. boiler room controller – which solution is better for my house.
What happens if the controller turns off the boiler but leaves the pump running?
This is deliberate and correct behavior in most controllers – it's called "pump overrun". After the burner is switched off, the remaining heat in the boiler's heat exchanger is properly transferred into the heating system, instead of staying in the boiler and heating the combustion chamber. Result: extended boiler lifespan, more efficient use of energy. The pump overrun duration is set in the controller, typically 3–5 minutes.
Which controller do you recommend for a standard family house with a gas boiler?
For a single-circuit system (one boiler, one external pump, one radiator circuit), the standard and reliable solution is the Adex midi Controller. For houses with two circuits (e.g. radiators + DHW tank) or an interest in weather compensation and greater setup comfort, we recommend the Adex Comfort R Controller or higher models in the Comfort series.
How do I find out whether my pump is integrated into the boiler or external?
Look at the boiler – if it's a wall-mounted gas boiler (a "combi" type), the pump is most likely inside. If the boiler is a standing unit (gas, oil, or solid fuel), look on the supply or return pipe near the boiler for a separate circulation pump – it looks like a cylindrical body with a motor, usually grey or blue (Grundfos, Wilo, DAB). If you see one, it's an external pump that the controller must be able to control.
Do I need an electrician to wire the controller, or can I do it myself?
Connecting the boiler room controller to the 230 V mains must be carried out by a person with professional electrical qualification (in accordance with local electrical safety regulations). Connecting the low-voltage sensors themselves (temperature sensors, room thermostat) can be handled by a technically skilled DIYer. In practice, then: sensors yourself, the power part wired by an electrician. The entire wiring must be documented and checked. Details can be found in the article Installing a boiler room controller step by step – what you can do yourself and what needs an electrician.
I have a wood boiler – is a controller with a pump a must for me?
Yes, for a solid fuel boiler without a storage tank, pump control is absolutely essential for safe operation. The controller must at least start the pump when a certain boiler temperature is reached (usually 60–65 °C) and stop it when the temperature drops (boiler has cooled down). Without this control, there is a risk of the boiler overheating at full power and the water in the system cooling too much at low outdoor temperatures. Solid fuel boilers also require return protection (minimum return temperature of 55 °C) to prevent condensation and corrosion of the heat exchanger.
Conclusion – a controller as an investment, not just an expense
A boiler room controller with pump control isn't just a "matter of comfort". It's a system component that protects the boiler from damage, reduces fuel consumption, extends the lifespan of the whole system, and improves thermal comfort in the house. Investing in a correctly chosen and correctly set up controller pays off within one to two heating seasons – and keeps saving money every year after that.
If you're not sure about the choice for your specific system, take a look at the comprehensive category thermostats, pumps and boiler rooms, where you'll find the entire range of ADEX products as well as other manufacturers. You can find more practical tips and answers to specific situations in the articles Frequently asked questions about thermostats and boiler room controllers and Maintenance and calibration of thermostats and controllers – how to prevent faults and extend lifespan.
The right controller is the heart of every boiler room. Don't skimp on it – it determines how efficiently and safely you heat your home for years to come.
Do you have a question about this topic?
Can't decide or dealing with a specific situation in your household? Write to us - we'll be happy to help.