AVANSA heating circulation pumps for radiators and underfloor heating

1. Installation length: 130 or 180 mm

The installation length is the distance between the pump's suction and discharge ports – in other words, the gap in the pipework into which the pump fits between two union connections. When replacing a pump, this is the most important dimension: the new pump should be exactly the same length as the old one. That way you simply swap it between the existing unions, without cutting or extending the pipework.

• Measure the old pump from the sealing face of one port to the sealing face of the other (without unions and seals).
• Result 130 mm → choose from the 15/6/130, 25/4/130 and 25/6/130 models.
• Result 180 mm → consider the 25/4/180, 25/6/180, 25/8/180, 32/6/180 and 32/8/180.
• This figure is often found directly in the type designation of the old pump (e.g. “…/180”) or on its rating plate.

A shorter pump can only replace a longer one if the pipework is modified or an extension piece is used – adding extra joints that may leak. A longer pump will not fit into a shorter gap at all without reworking the pipework.

2. Nominal bore (DN) and connection thread

The number at the start of the designation (15, 25, 32) indicates the nominal bore of the pump ports in millimetres. The pump is connected to the pipework via union connections whose nuts screw onto the thread on the pump body:

• DN15 – 1" thread (AVANSA 15/6/130),
• DN25 – 6/4" thread (all 25/… models),
• DN32 – 2" thread (32/6/180 and 32/8/180 models).

Do not mix them up: the pump's connection thread (e.g. 6/4") is not the same thing as the port bore (DN25), nor as the pipe size in the boiler room. If the original unions stay in place, what matters is the thread on the pump body – it must match the union nuts. When changing to a different size, suitable unions or reducers are used.

3. Head of 4, 6 or 8 m depending on the house and type of system

The head (delivery height in metres) expresses how much pressure resistance the pump can overcome. It must cover the pressure losses of your circuit – these increase with the length of the pipework, the number of radiators or circuits and the resistance of the fittings (valves, mixing valves, filters). It has little to do with the height of the house: in a closed system, the water that goes up comes back down again, so the pump does not “lift” water to the upper floor, it merely keeps it circulating.

• 4 m (25/4/130, 25/4/180) – smaller, simple systems: a flat, a smaller house, short pipe runs with fewer radiators. They also have the lowest power input (38 / 53 / 72 W).
• 6 m (15/6/130, 25/6/130, 25/6/180, 32/6/180) – a typical family home; a pump with a head of up to 6 m is usually sufficient for an ordinary family house. The most versatile choice, including when replacing an older pump.
• 8 m (25/8/180, 32/8/180) – larger and multi-zone systems, long pipe runs, bigger buildings and circuits with high resistance. They offer a much higher flow rate (115 and 160 l/min respectively), but also a higher power input.

Radiators vs. underfloor heating: a radiator circuit has shorter runs and lower resistance, so a 4–6 m pump is usually enough. Underfloor heating has tens of metres of pipe in each loop, a manifold with valves and often a mixing valve – the resistance is higher, so a 6 m pump is generally chosen for larger underfloor systems and 8 m for extensive areas or several manifolds. If in doubt, have a heating engineer size the flow rate and head – they will take into account the loop lengths and the required heat output.

4. Flow rate – how much water the pump moves

The maximum flow rate indicates how much water the pump can move when the system offers almost no resistance. Models with 4 and 6 m head reach 45 – 55 l/min, while the 8 m 25/8/180 and 32/8/180 reach up to 115 and 160 l/min respectively. For the 15/6/130 model, the manufacturer also gives values for the individual speeds: max. flow of 21 / 35 / 45 l/min and max. head of 3 / 5 / 6 m at speed 1 / 2 / 3. The real flow rate in a system is always lower than the maximum – it depends on the circuit resistance and the selected speed.

5. Setting the speed

The speed switch on the terminal box is the cheapest way to match the pump to the system. There is one simple rule: set the lowest speed at which all radiators or circuits heat up evenly.

• After installation and bleeding, start at speed 1 and on a colder day check that even the most distant radiators warm up.
• If the last radiator stays lukewarm, switch up one setting and check again after a few hours.
• A lower speed means lower power input – for the 25/6 models, for example, it is 46 W at speed 1 compared with 93 W at speed 3, i.e. roughly half the electricity over the whole heating season.
• A lower speed is also quieter – less noise in thermostatic valves and pipework.

6. Switching the pump with a thermostat

With a solid-fuel boiler, or when charging a buffer tank or hot water cylinder, the pump is often switched according to the temperature of the water in the pipe. This is what the AVANSA TH 2A clamp-on thermostat (230 V, range 20 – 90 °C) is for – it is attached directly to the pipe with a spring. It most commonly controls the boiler pump overrun, and in underfloor heating it is also used as a safety thermostat that switches the pump off. You will find an overview on the AVANSA thermostats page.

7. Noise

If you can hear rushing, whistling or gurgling in the system, the cause is more often in the system than in the pump itself:

• air – the system or pump has not been bled properly (typically after filling or replacement),
• speed set too high – the flow is noisy in the thermostatic valves; try a lower setting,
• low system pressure – check the pressure on the boiler gauge and top up with water if necessary,
• dirt and magnetite – a clogged rotor turns with more effort and more noise; a magnetic filter helps (see below).

Most common mistakes when choosing and replacing a pump

• buying a pump based on head without measuring the installation length – 130 and 180 mm are not interchangeable,
• confusing the nominal bore with the thread – a DN25 body has a 6/4" thread, not 1",
• fitting an oversized 8 m pump “just to be safe” in a small house – higher power consumption and valve noise where 4 – 6 m would do,
• mounting with the motor shaft vertical or against the flow direction arrow on the body,
• starting without bleeding – running dry or with air damages the bearings,
• replacing the pump in a sludged-up system without flushing and without a filter – the new pump will get clogged by the same sludge as the old one,
• a solid-fuel boiler without backup power – during a power cut, circulation stops while the fire is still burning in the boiler.

Solid-fuel boiler and accumulator tank

With a wood, coal or pellet boiler, the circulation pump carries heat from the boiler to the radiators or to the accumulator tank. Here the pump is a safety element: as long as the fire is burning, the water must circulate. The boiler pump is therefore often switched according to the water temperature by an AVANSA TH 2A clamp-on thermostat (range 20 – 90 °C), which switches it on once the boiler has warmed up and lets it keep running during the overrun period. In a system with a tank, the heating circuit after the tank usually has its own pump as well. Plan for power cuts in advance – an AVANSA boiler backup power supply keeps the pump running until the boiler has cooled down.

Gas or electric boiler with an additional circuit

Most wall-hung boilers have the pump built in. You need a separate circulation pump when another circuit leads off the boiler – for example underfloor heating via a mixing valve, charging a hot water cylinder or a branch to a second building. Each such circuit should have its own pump, and both the boiler and the pump can be switched by an AVANSA room thermostat.

Underfloor heating with a manifold

In underfloor heating, the pump pushes water through the manifold into loops tens of metres long, so the circuit has a higher resistance than radiators and a head of 6 m is usually chosen, or 8 m for larger areas. The pump is accompanied by a mixing valve that guards the water temperature and a TH 2A safety thermostat that switches the pump off if it overheats. The flow to the individual loops is set on the manifold – for example on an H.P.W.® brass underfloor heating manifold with flow meters. A heating installer can work out the number and length of the circuits in advance.

Several pumps in one boiler room

• Each circuit (radiators, underfloor heating, water heater) has its own pump and its own switching.
• With pumps connected in parallel, a non-return valve belongs after each pump so that one pump does not push water through the circuit of the other.
• Fit shut-off ball valves before and after each pump – replacement then takes a moment and without draining the system.
• A magnetic filter belongs in the return line before the boiler and pumps.

Other pipework

According to the manufacturer, the pumps are also intended for domestic water distribution, industrial circulation equipment and cold water and air-conditioning systems. For circulating drinking hot water, however, use the brass AVANSA CP 15-1.5 recirculation pump.

Why circulate hot water

If the water heater or boiler is a long way from the bathroom or kitchen, opening the tap first delivers the cooled water that has been standing in the pipe, and you have to wait for it to run hot. A circulation pump keeps domestic hot water (DHW) constantly circulating between the cylinder and the taps, so hot water is available at the tap almost instantly. It saves time as well as the water that would otherwise go down the drain while you wait.

Circulation pump vs. heating circulator

The AVANSA 15/…, 25/… and 32/… pumps drive heating water around the heating circuit (radiators, underfloor heating). The CP 15-1.5 circulation pump is designed for drinking water: it has a brass body, a ceramic shaft and a permanent-magnet rotor, which allows efficient, economical and trouble-free operation with a power input of just 25 W and quiet running.

Installation and operation

• The pump is usually installed in the circulation pipe upstream of the water heater or hot water tank.
• G 1/2" connection thread, 85 mm installation length, temperature range 5 – 95 °C, max. pressure 10 bar.
• The pump comes with a cable and plug – 220 V / 50 Hz power supply.
• Circulation increases both electricity consumption and heat losses from the pipework, because the water is constantly moving. That is why you should add a timer switch that runs the pump only when hot water is actually needed – in the morning and evening, for example.
• We recommend leaving the connection to the DHW pipework and the electrical supply to a plumber or electrician.

With a gas or electric boiler, a power cut switches off the heat source together with the pump, so the house simply cools down gradually. It is different with solid-fuel boilers: the fire keeps burning in the firebox, but the heat is no longer carried away to the radiators and the water temperature in the boiler rises rapidly. There is a risk of the boiler overheating, the water boiling and the heat exchanger being damaged.

The solution: an AVANSA backup power supply (UPS)

AVANSA backup power supplies are professional automatic UPS units designed to provide an uninterrupted power supply for solid-fuel boilers. When the mains fails, they switch to battery within 4 ms, keep the circulation pumps running and let the boiler cool down safely. The output voltage is a pure sine wave – the same as the mains supply in your home. When the mains comes back on, the unit recharges the battery by itself and keeps it on standby.

How to size the unit for an AVANSA pump

• Output: a pump is an inductive load and may need up to twice its rated power when starting. For loads like this, it is therefore recommended to use no more than 50% of the UPS's rated output. A 25/6 pump with a maximum input of 93 W can thus be covered even by the 300 W model; for two pumps or the 32/8/180 model (up to 270 W at speed 3), go for a more powerful unit. If the boiler electronics are also powered, add their power input.
• Battery: standalone units are supplied without a battery. A 12 V lead-acid battery is used (the 1050 W model needs 24 V – two 12 V batteries connected in series); gel batteries are not recommended. For optimum charging, the battery should have a capacity of at least 50 Ah; the maximum supported capacity depends on the model (e.g. 300 W up to 90 Ah, 700 W up to 150 Ah). Sets of a unit with a battery are also available.
• Backup time depends on the battery capacity and the load. According to the manufacturer, at a load of 100 W the unit runs for approximately 3.5 hours with a 65 Ah battery, 6.5 hours with 120 Ah and 8 hours with 150 Ah. At a load of 200 W, it is approximately 2, 3 and 4 hours.
• Location: a dry, well-ventilated place free from dust (including coal dust), out of reach of water and fuel – bear this in mind in a solid-fuel boiler room.

You will find the 300 W, 500 W, 700 W and 1050 W models, as well as sets with batteries, on the AVANSA backup power supplies page, together with a detailed guide to choosing a backup power supply for your boiler.