Powering the boiler from a UPS – connection
Powering the boiler from a UPS – connection
The backup power supply (UPS) is connected between the mains socket and the boiler. During a mains failure, it powers the boiler and the circulation pump from the battery. The required UPS output is the sum of the power input of the boiler and the pump. Click a number to open the matching product.
A number in the diagram takes you to the matching item in the list below.
Step 1: choosing the UPS
Step 2: UPS load
Backup power supply for the boiler and pumps
A power cut also puts a gas, pellet or wood boiler out of operation, because its electronics, fan and pump do not work without electricity. The set is intended for heating engineers, service companies and resellers offering customers backup for their heating. With solid fuel boilers, the main concern is safety; with other heat sources, it is keeping the house warm and protecting the system from freezing.
Installation procedure
- Find out the power input of all the appliances you want to back up – the boiler electronics and fan, the pumps, the controls and, where applicable, the zone valves.
- Choose a UPS with an appropriate power reserve according to the total power input.
- Select the battery according to the required backup time. Connect it with short cables of sufficient cross-section and with a fuse, and observe the polarity strictly.
- Place the UPS and the battery in a dry, ventilated room close to the boiler, out of reach of water and radiant heat.
- Plug the UPS into a mains socket and connect the boiler and pumps to its output. If the boiler is hard-wired, the conversion of the connection to a plug and socket must be carried out by a qualified electrician.
- Check the function by disconnecting the UPS from the mains as a test: the boiler and pumps must run without interruption, and the boiler must ignite correctly even when powered by the battery.
Choosing the right parts
- The UPS output should be chosen according to the total power input of the backed-up appliances, with a reserve. You need the reserve mainly for the starting currents of older pumps, which briefly draw more than during normal operation.
- Output waveform. Boilers with electronics and modern energy-efficient pumps require a pure sine wave supply. A UPS with a modified sine wave can cause faults or noise.
- Battery. Deep-cycle AGM or gel batteries are designed for longer discharging. Car starter batteries are not built for repeated deep discharging and quickly lose capacity.
- The backup time depends on the battery capacity and the load. You calculate the battery energy as the product of voltage and capacity – for example, 12 V × 100 Ah = 1 200 Wh. After deducting losses and a reserve against full discharge, a continuous load of 100 W gives roughly seven to eight hours.
- Charging. Check the maximum battery capacity permitted by the UPS manufacturer, so that the UPS can recharge it in time after a power cut.
- Compatibility with the boiler. Some boilers with ionisation flame detection are sensitive to polarity and earthing. Check the boiler manual for its requirements regarding a substitute power supply.
Most common installation mistakes
- An undersized UPS that overloads and shuts down when the pump starts.
- A car starter battery, or cables to the battery that are too thin and too long.
- A battery in an unventilated room or directly next to the boiler.
- Appliances unrelated to heating backup also connected to the UPS output.
- A UPS installed without testing a real power cut.
- A hard-wired boiler connection modified without a qualified person.
Commissioning and maintenance
Charge the battery fully before first use. Check the backup function with a test power cut at least before every heating season. Check the tightness of the terminals and the condition of the battery; replace the battery at the interval recommended by its manufacturer, because its capacity gradually decreases with age.
Frequently asked questions
How long will a UPS keep the boiler running?
It depends on the battery capacity and the power input of the backed-up appliances. With a smaller load and a larger battery, the backup lasts several hours.
Can a heat pump be backed up this way?
No. The power input of a heat pump compressor far exceeds the output of such units. Only circulation pumps and control electronics can be backed up.
Why is a UPS particularly important with a solid fuel boiler?
Burning fuel cannot be extinguished immediately. If the pump stops during a power cut, the heat from the boiler has nowhere to go and there is a risk of overheating. The UPS keeps the water circulating until the fuel has burnt out.
Does the UPS also protect the boiler against voltage fluctuations?
To a certain extent, yes, depending on the type of UPS. Check the specific protective functions in the technical documentation of the selected model.
What to order for backup power
You will find the complete range in the Backup power supplies section; for a typical boiler with a pump, the Avansa 500 W or the Avansa 500 W + 46Ah battery set will do the job, and you can choose the backed-up pumps in the Pumps for heating and water category. Registered partners can see wholesale prices after logging in. We dispatch goods from our warehouse in Žilina and ship them throughout the EU.