Just bought a house with an older boiler. It's been working pretty well, but I need to replace a couple of zone valves. I am an electrician, and pretty handy with tools but I have no experience with boilers and don't really want to flood or blow up my new place. I can replace the valves, but I need more info on refilling and bleeding the system, as well as what, if anything, I need to do with the expansion tank. Thanks in advance for any info!
New house with boiler, need help!
- Thread starter Tony De
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To the extent possible, isolate the sections that will be opened up with whatever ball valves etc that are on the system, to limit the amount of water lost, and the amount of air that needs purging after the fact. There is also an isolating valve, usually between a pressure reducing/auto-fill valve that should be closed before opening up the system.
Some photos of the zone valve manifold and nearby valves might make this discussion easier.
Tap on the expansion tank- the side with the air valve should ring, the other half should thud. If the system pressure is between 12-15 psi (there's usually a meter on or near the boiler) when the system is tepid, not full-hot, and the expansion tank still rings on the air-valve side it's reasonable to assume that it's pre-charge is still in a reasonable range. Let's not create extra work.
Often there are air bleeder valves on the radiators/baseboards, and when re-filling the system that's where it makes the most sense to start purging air, if most of that zone was drained. Do this without the pumps running, and purge air until it's a steady stream, no hissing or spitting. You may or may not have to open the zone valve manually to fill the zone, depending on how it's all plumbed. Sometimes you'll have to manually open the zone valves and flush the zone, opening up what looks like a outdoor hose faucet near the manifold or near the boiler, and just run a large amount of water through the zone to get rid of the biggest amount of air before it will be able to get good flow with the pumps.
With the system cold, adjust the system to something like 12-15 psi. The pressure relieve/autofill is usually pre-set to the system pressure, some systems don't have an auto-fill, and it's always manual. If the pressure is too high, bleed some water until it drops. If it's too low, let more water in. Don't power up or re-fire the boiler until you've purged what air you can, and have set the intial pressure to the right range. Set the thermostats for the replaced zone valves higher to call for heat, then observe the behavior. If you're lucky you'll get at least some flow right away, and the system air vents will eventually purge the rest of the air.
Again, some pictures of what you have will allow more particular advice- every system is a little bit different, and sometimes those differences matter.
Some photos of the zone valve manifold and nearby valves might make this discussion easier.
Tap on the expansion tank- the side with the air valve should ring, the other half should thud. If the system pressure is between 12-15 psi (there's usually a meter on or near the boiler) when the system is tepid, not full-hot, and the expansion tank still rings on the air-valve side it's reasonable to assume that it's pre-charge is still in a reasonable range. Let's not create extra work.
Often there are air bleeder valves on the radiators/baseboards, and when re-filling the system that's where it makes the most sense to start purging air, if most of that zone was drained. Do this without the pumps running, and purge air until it's a steady stream, no hissing or spitting. You may or may not have to open the zone valve manually to fill the zone, depending on how it's all plumbed. Sometimes you'll have to manually open the zone valves and flush the zone, opening up what looks like a outdoor hose faucet near the manifold or near the boiler, and just run a large amount of water through the zone to get rid of the biggest amount of air before it will be able to get good flow with the pumps.
With the system cold, adjust the system to something like 12-15 psi. The pressure relieve/autofill is usually pre-set to the system pressure, some systems don't have an auto-fill, and it's always manual. If the pressure is too high, bleed some water until it drops. If it's too low, let more water in. Don't power up or re-fire the boiler until you've purged what air you can, and have set the intial pressure to the right range. Set the thermostats for the replaced zone valves higher to call for heat, then observe the behavior. If you're lucky you'll get at least some flow right away, and the system air vents will eventually purge the rest of the air.
Again, some pictures of what you have will allow more particular advice- every system is a little bit different, and sometimes those differences matter.
