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Remote BMS and boiler monitoring over a SIM: what to check

A cellular link can give a plant room its own route out, but only if the signal, the alarm path and the modem all hold up. This guide covers the checks that matter, including older GSM modems exposed to the 3G switch-off.

How a plant-room link works

A controller in the plant room, often called an outstation, reads the sensors. A gateway or cellular router connects it to the outside world. A supervisor on a server, or a cloud service, turns an alarm into a text, an email or a call. SimFalcon's Irish BMS page says a cellular link can give a BMS contractor a path that is unaffected by customer Wi-Fi passwords, LAN changes or broadband replacement [14]. The catch is a second route into the building, with its own signal, SIM and security to look after.

Why plant-room signal is often poor

Plant rooms tend to sit in basements, behind masonry or inside steel cabinets. Ofcom commissioned research on how building materials affect radio signals [9]. In a small house, foil-backed insulation and metal-coated double glazing together added 5 to 10 dB to the loss of signal entering the building. A plant room is a different building, but the same principle applies.

SimFalcon's Irish boiler page says plant rooms, basements and metal cabinets can reduce signal, and that although multi-network may help, antenna placement and locating the router outside an enclosure can be just as important [15]. Teltonika advises moving the antenna towards a window or outside the building, and keeping the connectors tight [5]. Teltonika publishes these ratings for its own 4G and 5G routers. Other makers use their own scales.

MeasureExcellentGoodFair to poorPoor
RSRP (signal strength)-80 dBm or stronger-80 to -90 dBm-90 to -100 dBmWeaker than -100 dBm
RSRQ (signal quality)-10 dB or better-10 to -15 dB-15 to -20 dB-20 dB or worse
SINR (signal to noise)20 dB or better13 to 20 dB0 to 13 dB0 dB or worse

Teltonika says drop-outs are possible in the last two bands [5].

Record the figures at the antenna's real position, before and after any move. Our weak or no network guide covers more.

Getting alarms out as SMS or email

An alarm can become a message in the supervisor or in the router. For Niagara 4, an SMS gateway maker documents routing an alarm class to a recipient component that passes alarms to its gateway. The gateway sends the messages over the mobile network and must be reachable from the station over the network [11]. Some routers can also send SMS or email on events such as mobile data connecting or disconnecting, or signal strength. Teltonika says its email needs an email account and network connectivity, while its SMS needs the active SIM [6].

What a multi-network SIM does and does not do

A multi-network SIM can register on more than one supported network. SimFalcon's coverage page says multi-network is not a signal booster and not a guarantee of the strongest signal [16]. It helps when one network is weak, not when all are.

If your gateway fails over between connections, check the health test. Teltonika's failover pings chosen hosts, treats the interface as offline if none replies, and as always up if no host is set [7]. Make sure a target is set.

Fixed or dynamic addresses, and who can connect

Whether you need a fixed address depends on who starts the connection. SimFalcon's Irish BMS page says the design depends on whether the BMS needs cloud connectivity, engineer access or VPN [14]. A controller that only sends data out needs outbound access. Engineers who connect in need more.

Providers can share one public IPv4 address between many subscribers using carrier-grade NAT, which the IETF says introduces “substantial limitations” in communications [8]. A connection started from outside may then not reach the site router. Ask your SIM supplier, SimFalcon included, how addresses are handled before you design around inbound access. SimFalcon says private APN and controlled-routing options are available for suitable business deployments [15]. Our APN setup guide covers the router side.

Secure the second route too. Ireland's National Cyber Security Centre, in its guidance on securing operational technology, advises multi-factor authentication for all remote access, a VPN gateway followed by a jump box, and removing, changing or disabling default accounts. It also says the network diagram should include all external connections, including vendor and backup links [12]. A plant-room router with its own SIM is one. The guidance covers operational technology in general, so apply it in proportion to the site.

Older GSM modems and the 3G switch-off

ComReg lists heating systems among devices that may be affected by 3G retirement, as guidance only, and advises checking the device or contacting the supplier [1]. Vodafone switched off 3G in October 2024 [1]. Eir is retiring 3G from 1 October 2026, in phases over a number of weeks, starting in Donegal [1][13]. GoMo and Lyca Mobile customers are affected too, because those brands use the Eir network [1][4]. The radio inside the modem decides the outcome, not the age of the boiler.

Radio in the modemEffect of the 3G switch-offNotes
2G / GSM onlyDoes not rely on 3GAsk your network about its own 2G plans.
3G onlyLoses service when 3G ends in your areaNeeds a 4G modem or replacement unit.
2G and 3GMay fall back to 2GComReg says such devices keep making and receiving calls over 2G, but data services are affected [1]. Test any SMS alarm.
4G or 5GNot likely to be affected [4]Check that the device supports the bands the network uses.

A new SIM cannot add a radio the modem lacks. Our 3G switch-off guide has a device check.

Watch for dial-in modems too: older sites may be reached by dialling a GSM number to open a data call (circuit-switched data). In the Netherlands, one supplier's notice about that service ending on 2G says that, if data transfer is still needed, such modems must be replaced with ones that support internet-based data over GPRS, 3G or 4G [10]. It is a Dutch notice, so ask your own supplier what applies here. If you also look after sites in the UK, Mobile UK says all mobile providers have confirmed to the UK Government that they do not plan to offer 2G and 3G beyond 2033 [2], and that some older IoT devices rely on 2G, sometimes as a back-up [3].

Checklist for facilities and M&E teams

  1. List every remote link: controller, modem or router model, radios (2G, 3G, 4G), SIM, network, and what it carries (SMS, dial-in data or IP data). Mark 3G-only and dial-in units for replacement first.
  2. Measure signal at the antenna and send a test alarm end to end. File both results with the date, and repeat the test after any SIM, router or firmware change.
  3. Name who receives alarms, who is next, and who owns each SIM contract and renewal date. A prepaid SIM that runs out of credit can stop alarms without warning. SimFalcon says plans are billed annually, or monthly for business volumes [17].
  4. Put the link on the network diagram, change default logins, and use multi-factor authentication and a VPN for engineer access [12].
  5. Agree who supports what. SimFalcon says it focuses on connectivity and can work with the controls contractor [14]. Dashboards and engineer access can raise data use [15].

Where SimFalcon fits

SimFalcon says it supplies managed IoT connectivity for commercial heating and remote mechanical systems across Ireland [15], and lists multi-network connectivity and private APN options for suitable BMS deployments [14]. See its BMS SIM page, boiler and plant monitoring page, pricing and coverage. SimFalcon asks for the device model, Eircode or county, quantity and what the equipment needs to send or receive [15]. Send those via the contact page.

Sources

Frequently asked questions

Why is mobile signal weak in a plant room?

Basements, masonry and steel cabinets weaken mobile signal. In an Ofcom-commissioned study of a small house, metal-coated glazing and foil-backed insulation added 5 to 10 dB of building entry loss. Moving the antenna towards a window or outside the building, or the router outside an enclosure, is a sensible first step.

Does a multi-network SIM fix poor plant-room signal?

Not on its own. SimFalcon says multi-network is not a signal booster and does not guarantee the strongest signal. It helps when one network is weak at the site, not when every network is weak.

Do I need a fixed IP address for remote BMS access?

Not always. A controller that only sends data out to a cloud service needs outbound access, while engineers connecting in need more, such as a VPN or another controlled design. Ask your SIM supplier how addresses are handled.

Are old GSM modems affected by Eir's 3G switch-off?

It depends on the radios inside. A 3G-only modem will lose service as 3G is retired in its area. Eir is retiring 3G from 1 October 2026, starting in Donegal, and ComReg lists heating systems among devices that may be affected. ComReg says devices that can only use 3G and 2G keep making calls over 2G, but their data services are affected. A modem that only uses 2G does not rely on 3G.

How should I test BMS alarms sent by SMS or email?

Raise a real alarm from the sensor or point, send it to a named person, and record how long it takes to arrive. Repeat the test after any SIM, router or firmware change.

Questions about connectivity for your equipment? Talk to SimFalcon or ask Engineer Support.

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