Hot Water Boiler purge Options

After draining the boiler for servicing or installing a new boiler, it will need to be refilled and purged. There are many ways this process is implemented, depending on the contractor's general practices, the age and type of the existing system, or the parts available at the time.

First, let's start with some common misconceptions about purging.

System must be purged with hot water - False, it does not matter whether cold or hot
System must be purged with cold water - False, it does not matter whether cold or hot
System must be purged with the water flow the same as it flows when heating - False, it does not matter the direction of flow
Each return pipe needs its purge setup - False, fittings can be saved looking at optional piping practices
It is best to put the end of the purging hose into a bucket to ensure you always get all the air out. This is not needed, but it's not a bad idea either. The problem is that you can never purge all the air from the system. There is oxygen in the water you are purging with. After purging to destroy the rest of the air, the water should be heated and flow through an air eliminator
Systems should be purged every year - Nope, if piped properly, the initial purge should be sufficient. The rest of the air, the boiler, and components can be removed if all components are in the proper location.

Let's start with a common way of applying purging practices from the fifties. All zones or loops had their purge set up. It worked well, but at today's prices, it's a waste of fittings and money. When the zones were purged, you had to move the hose from one zone drain to another.

A newer way of setting up purge stations is to install a drain on the boiler supply, shut-off valve, and ball valves on all returns. While return ball valves are optional, they enable zone isolation. There is no longer a need to move the hose from one drain to another within the separate zones. Another advantage is that if the components are placed in the correct locations, you can isolate the supply to service the PRV, backflow preventer, air separator (if used), vent (if used), circulator(s), flow checks, or zone valves without having to purge the system if refilling is done properly. This means opening the valve above the closest circulator to the air separator one at a time. Turn on the circulator. You will hear the air coming back and venting; move to the next, then the next, until you are done. You will not have enough air to stop the flow, so the boiler will remove the small amounts per zone.

Lastly, many boilers today are piped with primary/secondary piping. I believe the best approach is to install the purge valve and drain on the boiler piping. All the zones and the boiler may be purged through a single drain.
To purge, you close the valve above the drain and all the zone ball valves. Open the drain and open a single zone at a time until all zones are purged. Open the valve on the boiler supply to bring water in from the feed to purge the last little bit of pipe.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, and installations should be reviewed on a per-job basis. Any work on your heating system should be performed only by qualified, experienced personnel. Comfort-Calc or its personnel accepts no responsibility for improper information or application, damage to property, or bodily injury from applied information found on this website.