Furnace Automation and Safety by Design

We’ve previously mentioned that heating systems are significantly automated. Safety systems automatically avoid dangerous situations. Sensors and controls on furnaces provide a constant hot water supply. This is a simple fact of modern life, that you can own a facility, set a temperature, and forget there are entire rooms dedicated to providing comfort until it breaks. In this post, we’re going to look at the equipment that supplies water, and prevents boilers from becoming steam fueled rockets.


Before we begin, we need to address a little disclaimer:

All Heating Solutions are Unique. Various pairings of hardware may leave your system configured differently than our example setup. We are going to talk about a heating system that detects the water level, supplies water, and detects when the water detector fails. Some configurations may be more or less complex.

Getting Water In

All boilers need to get water in a regulated manner. We can’t just run a cold water pipe straight into the heat exchanger and expect things to be safe or efficient. Cold water would constantly be flowing in, which would eventually chill the water in the storage tank. The furnace would always be running to keep the water inside it hot. If the external water supply were ever cut off, the furnace could burn its way clean through its casing. The simple solution, is a really bad one.

McDonnell & Miller Residential Water Feeder
To control the input flow of water, we use a Water Feeder. It does what the name implies. It’s triggered electrically or mechanically to open and feed water into the boiler. Older feeding mechanisms were mechanical and prone to seizing up. Many homes and facilities would have manual ones requiring someone to push a button or pull a lever to make hot water. Today, most systems are electronic and self managing. Our water feeder is little more than a very special valve, that takes orders from the rest of the furnace.


Measuring The Water Inside

Many systems will use a Low Water Cutoff (LWCO) to control the water feeder. This is as sensing device that determines how much water is in the furnace at a given time. When it detects a lack of water, it reports that to the furnace’s controller. The controller can either trigger the water feeder or shutdown the system. Its common sense that it can call for more water, but the more important feature, is triggering a shutdown. If your system develops a leak, water would flow in, water would flow out, and the furnace would fire until the heat exchanger glowed red hot, likely a few thousands of degrees hot. If it called for water AGAIN, that water would hit the exchanger, flash into steam, and launch the furnace across the room in a ball of steel, fire, steam, and death. Your humble LWCO lets the system run itself and prevents disaster.

McDonnel & Miller LWCO
There are however, scenarios where an LWCO can fail. The cut off device is usually in part, a mechanical flapper or float device. If that seizes up due to age, corrosion, or just hard water build up in the pipes, it’ll send a bad reading. The bad reading can turn your mechanical room into a private, indoor pond if nothing stops the water feeder from feeding. At the same time, this can cause your circulator pump to run when there’s no water coming into it. The furnace can run when the water isn’t even staying in it. We’d be back to square one, without one more sensor.


Grace in Failure

Low Water Cut Offs are close relatives of Flow Detectors and Flow Meters. Where LWCO’s measure the amount of water present, a Flow-sensor uses the same type of paddle, but detects whether water if flowing. Some can read the speed and direction of flow as well. This second sensor can be used to control the circulator pump and to verify that the LWCO is working correctly. Under normal circumstances, it signals the pump to boost pressure. If the furnace runs, but no water flows, the system can shut down, knowing that something has gone wrong rather than have the LWCO signal for water it will never get. This will extend the life of the equipment and allow for quick detection of leaks at the furnace itself. It also keeps your  facility in one safe, functioning piece.

McDonnel & Miller Flow Switch
Not quite a LWCO.

That is, three parts we’ve talked about. What about the impact on repairing things if any of them fail? The water feeder is probably the biggest pain, replacing it requires cutting off water to the boiler, draining water, and potentially cutting pipes. LWCO’s and Flow Sensors however, are much easier to handle. In large part, these just screw on to T-Connectors so they can dip their sensor into the water. In many cases, it should be a simple matter of unplugging, removing, and replacing. If you’re using an older style cut off device, it may be more complex. The mechanical cut offs could be integrated with the feeder mechanism. If your furnace is that old, it may be time to upgrade with some modern sensors and controllers.

 The Complete System

If the failure is due to hard water, and the connected build up of calcium and minerals in your pipes, it’s worth noting that this issue can be fixed in the future. Hard water is bad for your entire heating system. A simple water softener can remove the minerals and make your system all the more reliable for it.


As always, a message from our sponsor:

Is your ‘low water cutoff’ a tad.. high? Is it filling your mechanical room with water and still reading ‘low water’? Does your flow meter insist there is no flow, even under a thousand GPM flood? It sounds like your system needs some new parts.


At Procure Inc, we pride ourselves on offering great prices, fast shipping, and a massive variety of parts. You can order a part today, and have it at your doorstep tomorrow. You can call us for a decades-old piece of hardware, and we’ll do our best to hunt through warehouses across the world to find a new, compatible part for your system. We also stock major brands such as Mcdonell & Miller, to provide new parts as soon as you need them.

Did we get something wrong?

Is there something you want us to cover?

Let us know in the comments below or email: sales@procureinc.us.


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