How to Test Your Steam Boiler Mechanical Low-Water Cutoff

Probably one of the most common low-water cutoff controls used on residential steam boilers is the McDonnell & Miller Model 67. It’s a mechanical control that uses an internal float to monitor your boiler’s water level. A drop in water level lowers the float, activates a switch and shuts down the burner as a safety measure. Otherwise, without enough water, a boiler can dry-fire and create a dangerous condition. (See last week’s post for more on why we use low-water cutoffs.)

McDonnell & Miller # 67

All mechanical devices are subject to failure at some point. The low-water cutoff can accumulate rust and sludge that impedes the movement of the float. If too much debris accumulates and the float can’t drop during a low-water condition, the control can fail to operate when you need it most.

A simple weekly test you can do yourself can make a huge difference in the reliability of your low-water cutoff. Combined with a more thorough annual maintenance and scheduled replacement (every 10 years), you can be confident that your low-water cutoff will be ready when or if you need it.

Weekly maintenance involves “blowing down” or flushing your low-water cutoff by opening the lever-operated ball valve to flush out the sludge, rust or other debris.

Here’s how:

1.     You’ll want a 2 – 5 gallon bucket — preferably metal. The water you’ll be flushing is VERY HOT and can deform a plastic bucket.

2.     Verify the boiler water level is at its normal level. Adjust it if necessary by activating your water feeder or opening the manual fill valve.

3.     Turn up the thermostat so the boiler’s burner is firing during the test.

4.     Open the valve on the bottom of the low-water cutoff completely.

5.     Watch the water level as it drops in the gauge glass. (This is the glass tube on the side of your boiler that shows the water level.)

6.     As the water level drops to near the bottom of the gauge glass, the low-water cutoff should shut down the burner. (If it doesn’t, have it serviced immediately.)

7.     Close the valve and refill the boiler to its normal water level.

8.     The burner should relight.

9.     Reset the thermostat to its normal setting.

That’s all there is to it. Feel free to comment if you have any questions or would like to share your low-water cutoff experience. Good luck!

Hydronically yours,

Wayne

# 6 — Cleanliness: Why a hydronic heating system is cleaner than a forced air system

We've made it to installment #6 of the Top 7 reasons why a hydronic heating system is a better choice than forced air — Cleanliness. I hope you're still with me.

A forced air furnace with its blower and duct system will stir up and move dust, pollen and other impurities throughout your home. Some will remain airborne and inhaled while others will land on surfaces and leave a layer of dust that can again become airborne during cleaning. Then the cycle continues. Some of those impurities come to rest and cling to the inside of your air ducts.

Whole industries have sprung up to prevent and remediate the issues created by the "burner and blower" concept of heating. The sale and installation of HEPA filters, UV lights and electronic air cleaners have produced plenty of revenue enhancement for the furnace guys. And it seems duct cleaning services are being offered by everyone with a shop vac — from handy men to furnace guys to cleaning outfits. You gotta admire them, though — invent and sell a heating system that pushes dirt and allergens around your house, then offer add-on solutions to fix it. Hmmm.

As we've discussed in previous installments of Heidronics, your hydronic heating system uses a completely different heat delivery method. Pipes and tubing deliver heat from your boiler to your rooms without stirring up a trace of dust. The radiators, panels and convectors deliver their gentle heat without blowers or fans. The result is a cleaner indoor air environment with less airborne dust and allergens. You'll also find you need to dust less. And, of course, you'll avoid the added expense of replacement filters and duct cleaning.

Another hydronic advantage, especially for low-temperature radiant systems like in-floor or ceiling radiant, is a reduction in dust mite concentrations. Studies have shown that dust mite populations are significantly lower in homes equipped with low-temperature radiant heating. They've also shown a lower incidence of allergic reactions to dust inhalation. You'll find more detailed information at environmental ergonomics expert Robert Bean's website healthyheating.com.

Next week I'll wrap things up (and maybe dispel a myth) with a discussion about humidity. You may be surprised.

Heidronically yours,

Wayne