Danfoss Boiler Energy Manager BEM 5000

[fridgability]

Hi folks, my first post here.

My wife's folks have a Gas CH fully pumped system to which has been added a Danfoss BEM energy manager.

For some while they have had a problem with the pump continuing to run while the boiler is timed off.

I have checked that the pump is in fact getting its feed from the BEM by disconnecting it while the boiler is off, so that I know that it is not picking up a feed from elesware. in addition I have checked the sensors by means of the test points TP4/TP7 and TP3/TP7 and got sensible values. 22deg C outside and 45deg C return.

I have also switched off the pump over run timer switch which stops the pump the instant the boiler cycles off.

I can set the boiler timer to switch off the system and the pump stops but some time later it starts again even though the boiler is timed off.

This has only started since a thunder storm a while ago and it is possible that the unit has been damaged. However if any one has any suggestions I would be most gratefull.

Also if any one knows where I could obtain a replacement or an alternative that would also be most useful

 

[Peter Wingfiewld]

The BEM is pretty reliable IT. Its the best weather-compensated boiler control made apart from that costing zillions by Honeywell. The problem is no-one especially Danfoss, understands the thing. I have just gone over mine expecting it to be useless and my old Avometer helped a lot, plus the installation circuit diagram from the internet. That has a summary of how is supposed to operate too/.
My first answer is the pump is designed to stay on for a period when the demand system is over to off. This is so its doing its job emptying the boiler of hot water. The system then stops the pump power. Its under control of the BEM not the thermostats nor the boiler. Then the heat is put to use in either the radiators or the hot tank circuit. Only their Randall design engineer understood that as its crazy to a conventional plumber or electrician. Danfoss never understood how good their Randall engineers were.

If the actuator valves break down, the BEM stops controlling. You can tell how the actuators are by a light signal LED (2 on front p[anel) when the programmer attached calls for heat of CH or HW. If the actuators are ok these LEDs light up.

The 2-port valves for the HW and CH (mine are Honeywell) have a motor, supplied via the BEM 5000 PCB and monitored by a sensor to a microswitch in the valve actuator head. Microswitches have a life and eventually fail. The motor itself rarely fails but it has a crappy kind of gear-drive that could wear out...

If the microswitch fails the appropriate LED of the BEM stops lighting. its power is fed via the microswitch. The LED signal is actually put there to tell the CH or HW is in delivery mode. Its role to signal microswitch failure was never documented.

Presume the BEM 5000 is ok and turn off all power. Remove both 2-port actuator heads off their metal valve works. 2 small star-head screws. then 2 more to secure actuator. No need to remove the pipes and valve nor to drain system. Check the motor lever is self-shutting by moving the lever against a spring. check the connections to the 3 wires to miocroswitch when you press the microswitch button. At auto-close one will be connect-link Probably replace actuator after 5 years life and mostly the HW valve one works hardest so more likely to fail.

NOTE
If any of you threw out your BEM 5000 Im pleased to give it a good home and can then repair my own at circuit-level <[email protected]>

 

[Dan Robinson]

Did the flirking big red warning not appear telling you this was a 4 year old thread?

 

[Biggles..]

Maybe Honeywell designed the warning triangle and big red warning the forum now use???

 

[Dan Robinson]

That has really traumatised you hasn't it

 

[Peter Wingfiewld]

Hi all and Shabani. I know the warning says this thread is old, but thats what the internet is all about !

My item shows how you can find a fault very reliably without a Heave-ho its junk. there seems too much of that talk here.

People with electronic controls will need to know about diagnosis of their controls. From my experience, Danfoss dont care about customers when their kit is needing service support. They cant even supply a repair engineer manual nor any circuit diagram for the BEM 5000.

I have diagnosed heating servicing things ok as a complete amateur from days when I installed Danfoss Theta, another British weather-compensated proportional boiler controller of 1960's era. I managed two of them installed. It did just have those new fangled "transistors" too . That had a 3-port Danfoss mixing valve feeding HW and CH circuits, fed by selectable fixed comfort, user settings and a Sangamo Weston clockwork timer.

There again the key issue to system failure lifetime was the valve actuator. It had again travel-limit microswitches, also a mobile potentiometer contact link with wiper on a track following the physical valve position. The microswitches failed thus to stop the actuator motor driving the valve. There were periodically torn sensor wires in the actuator head. I replaced the actuator once or twice. Sometimes the actuator link-wire fatigued due to flexing and so gave no potentiometer sensor connection. That kind of actuator valve disappeared from current production, so I replaced the microswitches, very easy standard parts. I replaced the flexy wire link with a cutting of mylar-printed-circuit I had from scrap. The Danfoss actuator then went on fine and didnt need replacement again ever until after nearly 40 years, I had no more responsibility for it.

The Design-centre Prize-winning Drayton Theta Proportional Control panel once after 30 years needed a checkout. The Drayton company couldnt give me any circuit - just as now with Danfoss. It wasnt difficult job with a test-meter, component chart and lots of components 1% grade. I had no-one in the building at that time and experience with electronics, so just renewed everything on the PCB as the original component value before and it worked again a treat. It lasted from 1973 to 2010, when the building changed hands. Everything in IT build-quality is now much more reliable.

Good circuit design is pretty simple to service if you understand the logic going on. A bit more complex task to do with flow-soldered ICs and multi-layer PCBs nowadays but shorts dry-joints power rectifiers and diode-failures can be identified readily. We need service engineers who are savvy with how conrols work, also how they fail and a sense of component lifetimes. This set of notes is intended to show how good service engineering logic can be done.

With a sophisticated modern building, low-mass boilers, pipework, Zones, etc and energy management, its going to be difficult to swap one older system of control for another just because an engineer with the right thinking might not be around nor even any repair circuit or servicing advice. We all have to come up to repair engineer standard not thinking invariably like a garage mechanic. Maybe you cant just replace a Ferrari if It came from China ?

Back to the BEM 5000 history. Drayton had disappeared; Randall had another weather-compensated boiler control I used. Danfoss took over Randall to get into the British low-cost heating controls market. Under Danfoss It evolved into the BEM 5000. Danfoss then threw out their best small low cost controller not understanding what it was nor how to sell the idea properly into the boiler installation marketplace. Things in low-cost heating are different now, but there still isnt anything like performance of the BEM 5000, with boiler heat-saving and weather compensation at a reasonable cost so its time might have come round again !

Danfoss need to know they have to start sharing information for servicing engineers

My BEM 5000 went through 3 revisions of the PCB. There ought to be records somewhere.

Does anyone know what happened to the Randall design office files with their circuits and specification data, when Danfoss took over ? Danfoss claim they just dont know.

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