Danfoss BEM 4000 Boiler Energy Manager


The Boiler Energy Manager (BEM) is an electronic controller which can be added to almost any central heating system to eliminate unnecessary boiler cycling and improve boiler seasonal efficiency.

The BEM 4000 consists of an electronic controller, an outdoor temperature sensor and a strapon flow temperature sensor. It can be used in conjunction with a room thermostat (utilized as a frost stat) and TRVs. Boiler performance is improved when the flow temperature is varied according to the outside temperature. The outside temperature sensor should be mounted on the coldest elevation of the building away from opening windows and the boiler flue.The flow sensor should be fitted within 6 inches of the boiler outlet on the flow pipe, or on low-water content boilers it can additionally be fitted between the boiler and the bypass. A cylinder thermostat should be fitted as normal. All diagrams show Danfoss programmer and thermostats, but others can be used. In all cases, if a room thermostat is to be utilized as a frost or lowlimit thermostat, connect to terminals 3 and 11.

In Figures 11.2 and 11.3 two boilers are shown – one with pump overrun and one without. Select diagram as appropriate, remembering to insert Link 2–4 when using boiler without pump overrun.

Gravity hot water pumped central heating 300x184 Danfoss BEM 4000 Boiler Energy Manager

Figure 11.1 Gravity hot water, pumped central heating

Fully pumped system with two motorized zone valves 300x169 Danfoss BEM 4000 Boiler Energy Manager

Figure 11.2 Fully pumped system with two motorized zone valves

Fully pumped system with mid position valve 300x162 Danfoss BEM 4000 Boiler Energy Manager

Figure 11.3 Fully pumped system with mid-position valve


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  1. I have a very old Danfoss boiler energy manager (model unknown 20+years) with a outside thermostat. It has 4 lights – boiler,tap,pig and on. It appears that the outside thermostat is vying with the indoor thermostat eg: the boiler tries to ignite but can’t always do this and the red light goes on/off multiple times and makes a crackling noise. I would very much appreciate your help to resolve this problem.

    • Hi Geoffrey,
      This Danfoss boiler energy manager of yours sounds like the same one I have had since the late 1970s – BEM 4000.
      Your fault sounds similar to the one I had back in 2004 when the BEM unit made a buzzing / clicking noise and the boiler failed to operate correctly. I identified the problem as a faulty relay (1 of 2 ) on the printed circuit board of the BEM.
      A replacement relay was purchased from Farnell , part number 626004 , and I fitted it myself (soldering iron job). No further problems have occurred since.
      Hope this helps.
      Ken Hall

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