Saturday, October 20, 2012

Getting Steamed Over Boilers

After crawling in another crawl space for the second time this week, installing a make up air system, I got a call that a boiler would not shut off. To make this harder, the thermostats, all three of them, were replaced a few months ago. The customer complained that it was 78 degrees in her tri level home; hence the three thermostats. The customer ranted (and I can't really blame her) that the thermostats were at fault. However, a professional doesn't have the luxury of replacing parts based on belief. We need good hard evidence that a part is failing. You could get a volt meter out and test for voltage, but try this first...

If there is more than one thermostat on a hot water boiler system, you have a zone system. This means there are multiple loops throughout your home called circuits, only these hold hot water to transfer heat into your home. They are very efficient and reliable and provide years of heat without complaint. Each thermostat controls a zone valve that allows water to flow from the return side of the circuit to the boiler and hot water through the loop. For the most part, these zone valves have a lever or some other means of letting you know they're working. In the case of the Honeywell valves, there is a lever that loses resistance when you push it if power is applied. Water also flows through the pipe and if it gets colder then much hotter, this means the valve is open. If the valve is closed, there will be resistance on the lever opening it. This was the case on all three zones, tested individually. A look at the temperature gauge turned up something interesting, reading 230 degrees on a hot water boiler. The aqua stat on the boiler read about 190, so this was out of calibration a bit. 160 to 180 degrees is good for most boilers and they should be no more than 12 p.s.i. pressure. 

However, why was heat still getting upstairs? Well, the answer finally hit me as I left the driveway after turning down the aqua stat. Heat was getting up through the supply side through the pipes, driving the pressure close to 25 p.s.i. and transferring that heat into the living space. When it gets that hot, heat is going to move from a hotter space to a cooler one. This is another reason to keep your cool, and not jump to conclusions when diagnosing a boiler. Maranatha! 

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