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Weather Compensation & Load Compensation Controls

How Weather Compensation Works

Weather Compensation (WC) controllers work by adjusting the boilers flow temperature in relation to the outside air temperature, insuring the lowest possible flow temperature is delivered into the heating system at all times. This helps the boilers operate in condensing mode for longer periods of time, maximising boiler efficiency and saving energy consumption whilst increase comfort levels within the property.

An air sensor is fitted externally to the fabric of the building on a North or North West facing wall to avoid direct radiation from the sun. The sensor registers the outside temperature and sends this information to the boiler, the boiler uses this to determine what temperature the flow should be set to, as the outside temperature increases or decreases so does the flow temperature. The aim is to keep the inside temperature constant or within a set parameter controlled by the controller, set up correctly users would not notice the weather has changed outside.

Weather Compensation Curve and Slope

The heat curve is what most weather compensation controllers use to determine what temperature the flow should be set to in relation to the outside temperature. Adjustments to the heat curve and slope are to be made when setting up parameters within the controller, information can be obtained from a graph in the manufacturer’s instructions (MI’s) to understand what settings should be used. This may be a process of adjustment over some time to hit the sweet spot.

Installation of Outside Sensors

When installing an outside sensor, it should be placed on a North or North-West facing wall, 2 to 2.5m above ground level. It should not be placed above windows, doors, or ventilated outlets, and should not be immediately below balconies or gutters. The sensor should never be rendered over. A 2-core lead with a maximum length of 35m and a cross-section of 1.5mm2 should be used. 

How Load Compensation Works

Load compensation (LC) works by using an internal sensor to determine how much heat is required to reach its setpoint. When the difference between the actual room temperature and the desired room setpoint is considerably different the boiler will run at a higher flow temperature to increase the rooms air temperature, as the difference becomes less the boiler will lower the flow temperature to meet the desired rooms setpoint. This method of controlling the heating has a faster response time in comparison to weather compensation though will run hotter, increasing the kW output to achieve this.  


Most modern combi boilers are able to offer weather compensation or load compensation either by using the manufactures specific branded controllers, using a protocol called OpenTherm (OT) or by simply fitting an outside sensor to the boilers printed circuit board (PCB) and adjusting the parameters with in the boilers software.

Some system boilers and heat only or regular boilers also offer weather compensation, load compensation and/or OpenTherm which have two zones or more, this setup is slightly more complex where they require the heating zone valves to be changed from a S or Y-plan to a X-plan and may incorporate an additional module to control the temperature changes within the system from the boilers PCB. This setup is known as priority domestic hot water (PDHW)  and is strongly advised when upgrading to your next gas boiler.


Thermal insulation used within in the property is an important factor when setting up any weather compensated heating system, it determines what temperature the boiler would need to operate at to reach the desired target room temperature.

Poor thermal insulation would result in increased energy consumption, a higher heating curve and higher heat output. Improving the thermal insulation within walls, floors and loft areas is advised as this will reduce the heating curve and slope. Adding or upgrading pipe insulation around heating pipework under floors and in unheated spaces will help lower temperatures further.

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