How to choose a backup power source for your boiler and circulation pump

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Why to consider backup for the boiler and circulation pump

Power outages are a more common occurrence in Slovak households than one might initially think. Storms, faults in the power lines, planned outages of the distribution system, and even local tripping of circuit breakers can disconnect an entire house from the grid for several minutes to several hours. In a typical household, this usually means only the lights go out and the Wi-Fi stops working. In a house heated by a gas, electric, or solid fuel boiler with forced water circulation, the situation is different – without electricity, the boiler's control electronics, the flue gas exhaust fan, and the circulation pump that distributes heat to radiators or floor heating do not function.

In practice, this means that even if the house has gas and the boiler is technically functional, without electricity it simply does not heat. In cold weather, when the outage lasts longer, there is a risk of freezing water in the pipes, especially in some systems (particularly in floor heating with sensitive piping or in older homes without sufficient thermal mass). It is even more critical in buildings where heating is also connected to hot water heating or to technology (cottages, workshops, stables, breeding areas). That is why an increasing number of homeowners are choosing to install a backup power source (UPS) specifically for the boiler and circulation pump.

In this article, we will look at how such a power source works, which parameters are key when selecting one, how to calculate the required power and battery capacity, how the installation proceeds, and what to pay attention to so that the backup actually works when you need it. If you are looking for a quick orientation based on power, we also recommend a separate article "What backup power capacity do I need for my boiler?" – here we will address the topic in more detail and from several angles.

How a backup power source for a boiler works – the UPS principle

A backup power source for a boiler works on the same principle as a UPS (Uninterruptible Power Supply) used for computers and servers, only it is dimensioned and adapted for the needs of heating technology. The device is permanently connected to the electrical grid, through which its internal (or externally connected) battery is charged. The boiler and circulation pump are not connected directly to the socket, but to the output of the backup power source.

As long as the grid voltage is normal, the power source functions as a continuous switch – the current from the grid passes through the device to the appliance and the battery remains charged. At the moment the grid fails, the device's electronics detect this (typically within a few milliseconds) and automatically switch the power to the battery, creating an alternating voltage of 230 V using an inverter. The boiler usually does not even register this transition – the control electronics and the circulation pump do not restart, and heating continues without interruption.

It is also important to have the function of recharging after the power is restored – the power source automatically detects the return of the grid and begins to recharge the battery, so it is ready for the next outage. High-quality power sources also have battery status indication, audible signal when switching to backup mode, and protection against deep discharge, which disconnects the battery before it is irreversibly damaged.

Clean sine wave vs. modified sine wave – why it matters for the boiler

This is one of the most important, yet often overlooked parameters. A standard electrical grid supplies alternating current with a smooth sine wave. Cheaper backup power sources generate so-called modified (adjusted, stepped) sine waves – that is, a voltage that alternates at the same frequency, but its waveform is angular, composed of rectangular pulses.

For simple resistive loads (light bulb, electric kettle), this is not a problem. With boilers, it is different – the control electronics, frequency-controlled circulation pumps (especially modern pumps with electronic speed control), and some types of gas burners with electronic ignition react unreliably to distorted voltage. In practice, this is manifested as:

error messages on the boiler display after switching to battery power,
humming or vibrations of the circulation pump,
improper functioning of the pump speed regulation,
in the worst case, even failure or damage to the boiler control board under repeated load of distorted signals.

Therefore, for powering boilers and circulation pumps, backup power sources with a clean sine wave output (pure sine wave) are clearly recommended. All models of the Avansa series intended for this category – Avansa 300 W, Avansa 500 W, Avansa 700 W and Avansa 1050 W – work with a clean sine wave, making them compatible with all commonly used types of boilers (gas condensing, electric, solid fuel with circulation pump, pellet boilers) and electronically controlled circulation pumps.

How to determine the required power of the backup power source

The power of the backup power source is given in watts (W) or volt-amperes (VA). It is key to know the total power consumption of all devices you want to back up and to add a reserve for the so-called inrush current (the starting impulse of the pump motor, which can temporarily exceed the rated power by 2-3 times).

Typical approximate power consumption values for common devices in the boiler room:

control electronics of a gas boiler (without pump): 15 – 50 W
circulation pump of an older type (without electronic regulation): 60 – 120 W
modern electronically controlled circulation pump (e.g., energy-efficient): 3 – 45 W depending on the set speed
exhaust fan for flue gases in a condensing boiler: 30 – 80 W
circulation pump in combination with a three-way valve and zone control: together 80 – 150 W

In a typical single-family house with one condensing boiler and one circulation pump, the actual total power consumption usually ranges between 80 and 200 W, occasionally higher in larger houses with zone control and multiple pumps. We always recommend calculating at least a 30-50% reserve over the determined total, precisely due to inrush currents and possible future system expansion. A detailed procedure on how to measure actual consumption (e.g., using a simple socket power meter) can be found in the article "How to determine boiler and pump consumption for backup selection."

Avansa power recommendations – for whom they are intended

Avansa backup power supply range is divided by power to cover most common scenarios:

Avansa 300 W – suitable for a circulation pump alone or a small boiler with low power control electronics, or as a minimum solution for a simple system without additional devices.
Avansa 500 W – a universal choice for a standard condensing boiler with one circulation pump, most often recommended model for family houses.
Avansa 700 W – suitable where there are multiple devices in the boiler room at once (boiler, pump, fan, possibly also a circulation pump of a solar system) or where a higher power reserve is needed.
Avansa 1050 W – the most powerful model in the range, suitable for more demanding installations, larger houses with zonal control, or when additional small devices are to be backed up at the same time (e.g. control unit of a heat recovery system, small router for remote meter reading, etc.).

If you are unsure which power level to choose, a detailed comparison of the parameters of individual models can be found in the article "Comparison of Avansa backup power supplies by power".

Battery capacity and backup duration

The power of the power supply (W) determines whether the device is able to start and power the appliances. The battery capacity (given in ampere-hours, Ah, at a given voltage, typically 12 V) determines how long the backup power supply can run at a given load. A simple relationship applies: the higher the power consumption of the connected appliances and the longer the required backup duration, the larger the battery (or the more batteries connected in parallel) is needed.

Approximate calculation: a battery with a capacity of 46 Ah at 12 V represents an energy reserve of approximately 550 Wh (46 × 12). At a real load of about 100 W (boiler + circulation pump) and taking into account the inverter efficiency (about 85-90 %), we can expect a duration of about 4-5 hours. At a lower load (e.g. only an energy-saving electronic pump with a power consumption of 20-30 W), the duration can be extended to 12-15 hours. More precise tables and model calculations for various combinations can be found in the articles "How long will the backup power supply last during a power outage" and "What battery capacity is suitable for a circulation pump".

For households that want a "turnkey" solution without the need to separately purchase and connect an external battery, the practical choice is the set Avansa 500 W + 46Ah battery – it combines sufficient power for a standard boiler with a pump and also a battery with a capacity that can cover most common outages (in the order of hours), not just short-term grid flickers.

When to consider a larger or multiple batteries

If longer outages occur in the area (e.g. remote areas with weather-sensitive lines, cottages supplied by long overhead lines), or if you want to back up the boiler and also other devices (heat recovery, part of the lighting, router), it is worth considering a higher battery capacity or the possibility of connecting a second battery in parallel. When extending the backup duration, it is always important to consider that the battery must be fully recharged after an outage before the next one occurs – in the case of very frequent outages (multiple times a day), the charging speed is more important than the capacity itself.

Installation and connection of the backup power supply to the boiler

The installation of the backup power supply for the boiler is not technically demanding from an electrician's point of view, but it requires adherence to several principles to ensure reliable and safe backup operation.

Basic installation steps

The power supply is placed near the boiler, ideally on a wall or shelf in the boiler room, in a dry and well-ventilated place (batteries emit heat and possibly gases during charging, so a closed cabinet without ventilation is not recommended).
The input of the power supply is connected to a standard 230 V socket (a separate, easily accessible circuit is recommended, ideally protected by its own circuit breaker).
The boiler and circulation pump are powered exclusively from the output socket(s) of the backup power supply – not simultaneously from the grid and the power supply.
For models with an external battery, the battery cable is connected with attention to the correct polarity (positive and negative pole), and the screw connections are tightened to the recommended torque.
After installation, a test is carried out – disconnecting the power supply from the grid (e.g. by unplugging the plug) and checking whether the boiler and pump continue to operate without flickering or error messages.

Important warning: the backup power supply must not be connected directly to the distribution board in parallel with the grid without a suitable switching (transfer) connection – reverse feeding of the grid (so-called island mode) is dangerous for workers of the distribution network during outages and is also in violation of safety regulations. For simple power supplies such as Avansa, it is therefore always recommended to use a separate socket solution, not a permanent connection to the house wiring. A detailed step-by-step guide to the specific connection can be found in the separate article "Installation and connection of the backup power supply to the boiler".

Placement and Operating Conditions

Most backup power supplies are designed for operation in standard indoor environments with temperatures ranging from approximately 5 to 35 °C. In an unheated boiler room in a cottage, where temperatures drop below freezing in winter, the capacity and lifespan of a lead-acid battery may be significantly reduced – in such a case, it is worth considering placing the unit in a temperature-controlled space or at least in a thermally insulated enclosure.

Practical Scenarios from Everyday Practice

Over the years of selling and installing backup power supplies for heating systems, we repeatedly encounter several typical situations:

Scenario 1 – single-family house, gas condensing boiler, floor heating. The customer experienced repeated short outages (summer storms, faults in overhead lines). The solution was a Avansa 500 W directly connected to an outlet next to the boiler, with the pump and boiler powered from its output. During a test outage lasting approximately 40 minutes, the system operated without a single heating interruption, and the boiler display did not register any disruption.

Scenario 2 – cottage with a solid fuel boiler and a storage tank. Here, only the water circulation via the pump was critical (the boiler burns even without electricity, but without the pump, overheating and boiling in the system are possible). A smaller Avansa 300 W was selected, which safely covered the power consumption of one circulation pump and prevented critical overheating during a power outage while heating with wood.

Scenario 3 – larger house with zonal regulation, two heating circuits, two pumps. The total power consumption exceeded 150 W, and with a reserve for starting currents, a Avansa 700 W was selected. The customer also required longer backup during nighttime outages, so an external battery with higher capacity than standard was connected to the power supply.

Scenario 4 – house with home automation and heat recovery. In addition to the boiler and pump, the customer wanted to back up the control unit of the heat recovery unit and the router. Due to the higher overall power consumption (over 300 W) and the requirement for longer backup, the most powerful Avansa 1050 W with a larger battery was selected.

Common Mistakes in Selection and Installation

In dozens of completed projects, we repeatedly encounter several errors that can be easily avoided:

Underestimating the starting current of the pump – the customer selects a power supply exactly at the limit of the rated power, but during the motor's startup, the power supply is briefly overloaded and the protection shuts it off.
Selecting a power supply with a modified sine wave due to lower cost – the boiler runs, but the electronically controlled pump hums, or the boiler reports an error.
Underestimating battery capacity – the power supply has sufficient power, but the battery lasts only 20-30 minutes, which is not enough during longer outages.
Incorrect placement – the power supply in an enclosed cabinet without ventilation, or conversely, in a damp, unheated space, which shortens battery life.
Lack of regular testing – the power supply is installed and not tested for years; when a real outage occurs, the battery is already degraded and cannot last the planned time.
Simultaneous power supply from the grid and the power supply – incorrect wiring that can damage the power supply or cause a safety risk.

More about typical technical problems and their solutions can be found in the article Common Faults of Backup Power Supplies for Boilers and Pumps.

Maintenance and Battery Lifespan

Most backup power supplies for boilers use sealed lead-acid batteries of the AGM or gel type, which do not require electrolyte topping up and are maintenance-free in terms of regular operation. This does not mean, however, that you should not follow a few rules to extend their lifespan:

Do not leave the battery discharged for long periods – deep discharge significantly reduces the number of charging cycles.
The ideal operating temperature is 15-25 °C; extreme heat and cold shorten the lifespan.
It is recommended to perform a test at least once every 6-12 months by disconnecting from the grid and verifying that the device actually switches over and maintains the load for the expected time.
The lifespan of a standard AGM lead battery with proper use is approximately 3-5 years; it may be shorter with more intensive cycling (frequent outages).

A detailed guide on battery care, including signs that the battery is nearing the end of its life, can be found in the article Maintenance and Lifespan of the Backup Power Supply Battery.

Summary – How to Proceed with Selection Step by Step

If we were to summarize the entire selection process into a simple procedure, it would look like this:

Determine the total power consumption of all devices you want to back up (boiler, pump, possibly a fan or zone valves).
Add a reserve of 30-50 % to the total for starting currents and future expansion.
Choose a model based on the resulting number – for a standard boiler with one pump, a Avansa 500 W is usually sufficient, for smaller needs a Avansa 300 W, for higher consumption a Avansa 700 W or Avansa 1050 W.
Consider how long a backup during an outage is sufficient for you and choose the battery capacity accordingly – for a comprehensive solution, a practical choice is the set Avansa 500 W + 46Ah battery.
Ensure proper installation – a dedicated outlet, a ventilated space, no simultaneous power supply from the grid.
Test functionality regularly and monitor battery condition.

Frequently Asked Questions about Backup Power Supplies for Boilers and Pumps

Can a backup power supply power the boiler during a multi-hour outage?

Yes, but it depends on the capacity of the connected battery and the total power consumption of the devices. A standard set with a 46 Ah battery at a consumption of around 100 W can provide approximately 4-6 hours of operation. For longer backup, it is possible to connect a battery with higher capacity or multiple batteries in parallel.

Must the backup power supply have a clean sine wave, or is a cheaper modified sine wave sufficient?

For boilers and especially for modern electronically controlled circulation pumps, a clean sine wave is clearly recommended. A modified sine wave can cause error messages, pump noise, or in the worst case, damage the boiler's electronics.

Can I connect other devices, such as a router or lighting, to one backup power supply?

Yes, provided the power supply has sufficient reserve capacity and battery capacity. However, keep in mind that each additional connected device shortens the time during which the power supply can power the priority devices (boiler, pump).

How often should a backup power supply be tested?

We recommend a test at least once every six months to a year – disconnect the power supply from the grid and verify that it actually switches to the battery and maintains the load for the expected time. This prevents the unpleasant surprise of a discharged or degraded battery exactly when a real outage occurs.

Can a backup power supply for a boiler be connected by oneself, or is an electrician required?

Basic wiring via a dedicated outlet (grid to the power supply, boiler and pump from the power supply output) is safe even for an average user who follows the manufacturer's instructions. For more complex installations (multiple circuits, connection to a distribution board, higher power), we recommend consulting or having the installation done by a qualified electrician.

What happens if the battery in the backup power supply is completely worn out?

High-quality power supplies have protection against deep discharge, so the power supply itself is usually not damaged by a failed battery. It will be noticeable by a shorter backup time during an outage, or possibly by a battery fault indication. The battery can usually be replaced separately without the need to replace the entire device.

Conclusion

A backup power supply for a boiler and circulation pump is not an unnecessary luxury, but a practical insurance that can prevent the house from cooling down, freezing damage to the piping, or an uncomfortable boiler restart after every outage within a few seconds. The key to satisfaction is choosing the right model according to real consumption (not the lowest price), selecting a clean sine wave output, and sufficient battery capacity according to the expected outage duration in your area. The Avansa range offers several power levels from 300 W up to 1050 W, including a ready-made set with a battery, so both the owner of a small cottage with one pump and the operator of a larger house with zonal regulation can choose accordingly. If you are unsure which model exactly matches your installation, we recommend calculating the consumption according to the guide in the article How to Determine the Consumption of a Boiler and Pump for Backup Selection, or contacting our technical support directly.

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