The pump is an integral part of a central heating system, circulating the hot water through the network of pipes and to the radiators. An ineffective pump can lead to a variety of problems as well as making the heating system less efficient overall.
Although it is a part of the heating system which you may never have given much thought, if you are installing a new system, replacing a pump, or even replacing a boiler, it is something that requires your consideration.
Building regulations now state that any new system should be fully pumped, and this includes the upgrade of a system or a replacement boiler.
If you have an older semi-gravity system, you will need to upgrade the pump as part of the system or boiler upgrade, changing it to a fully pumped system.
How central heating pumps work
Older style central heating systems, known as semi-gravity systems use the natural convection of hot water to heat domestic hot water, while using a pump for the radiator circuit only.
When the hot water cylinder thermostat calls for heat from the boiler, water in the heating circuit is heated, and naturally rises into the coil running through the cylinder, indirectly heating the domestic hot water.
The pump is only engaged when the room thermostat calls for heat, and water is circulated through the radiators as normal. This means that when the central heating is on, so is the hot water; and although it is possible to heat the water only, it is not possible to heat the radiators independently of the hot water.
More modern systems use a motorised zone valve or valves, often fitted directly after the central heating pump, to divert the water to either the hot water cylinder or the radiators as required.
This means that both can be heated simultaneously or independently, and building regulations state that this is now the only acceptable system for new installations, or when replacing a boiler.
What types of pump are available?
There are a variety of different pumps available and most will do the job adequately. The specification of each pump can vary depending on the maximum water pressure they can withstand, and the size of the heating system (in terms of KW of heat output) they can support.
We can look at two products from Grundfos, a leading supplier of central heating pumps, as an example.
The Grundfos UPS 15/50 Selectric 130 pump can provide circulation of hot water for domestic systems, which have a heat output of up to 35KW. Like most standard pumps it has three variable speeds, which can be used to tailor the pump to your system requirements.
When setting up a pump it is advisable to put it on the lowest speed initially and increase as necessary if there is not enough heat to heat the radiators. In reality, most modern efficient boilers will require a pump to be set to the highest of the three speeds.
The pump comes with standard port to port fitting for ease of replacement, and would be more than sufficient for most domestic central heating systems.
The Grundfos ALPHA2 is a more sophisticated pump which incorporates Grundfos’ AUTOADAPT technology. Rather than having three speeds like most conventional pumps, it will analyse the heating system as it is used, and automatically adjust the pump speed to suit.
It will ascertain the optimum setting and will continually adjust speed to ensure it works most efficiently. It includes an integral pressure control system, and also a display which shows the pump’s actual power consumption in Watts.
How much do pumps cost?
A standard central heating pump like the UPS 15/50 will cost around £60, while a more advanced system such as the ALPHA2 pump could cost as much as £160.
Specifying a pump
Selecting the right pump can be difficult, and it is best to consult the person installing the heating system to make sure that the pump is adequate to circulate the water in your property to provide ample heat to all of the radiators.
If you have very high water pressure, or a particularly large house, you may need to buy a specialist pump to suit.
Replacing a central heating pump
Replacing a central heating pump is a relatively simple job which you can carry out yourself if you feel confident with DIY. The vast majority of pumps come with standard fittings and new washers so can be replaced without any changes to pipe work or connections.
If it was fitted correctly in the first place, your pump should have isolation valves installed either side so it can be quickly removed without the need to drain the entire system.
Make sure you turn the power off so that the boiler and pump cannot become active while you carry out the replacement. It is best to lay some towels or cloths around the pump area to catch any water spillages.
Once the old pump is removed, the new pump should be fitted in the same orientation, with the arrow indicating the flow of water pointing in the same direction as the previous pump. The electrical connections on a pump are usually simple, and just require the connection of live, neutral, and earth wires.
If you are unsure about any part of the replacement, or your pump was not fitted with isolation valves, it may be best to contact a professional plumber to carry out the replacement for you. This should cost around £140 – £160 including the new pump; although if the system needs to be drained down, it could cost an extra £200 or so.
Central Heating Pump Speed Setting
If you’re wondering whether you need to adjust the speed of your central heating pump, check out our article on Central Heating Pump Speed Setting – which will tell you everything you need to know.
If you are fitting a new central heating system into your home or upgrading an existing system, then it is probable that you will also be fitting a new pump. If you have entrusted the installation to a professional, they should be able to specify a pump for you which will provide adequate circulation to heat the radiators efficiently.
If you are choosing the pump yourself, make sure you select a model which can cope with the heat output requirements of the heating system in your property.