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DanDaMan 12-11-2010 12:23 PM

Need help fast please re hydronic boiler water supply and backflow
Stupid me left my garage door open yesterday for about 4 hours during minus 15C weather without having the garage furnace on. In my garage I have my hot water heating boiler along with major 1/2" copper piping running all over the place. After 4 hours I by chance was in the area and saw frozen water on top of the pipes. I instally closed the garage door and fired up the garage furnace. Sure enough about 10 minutes later one pipe started to spray water everywhere. Fortunately a shutoff was right in front and that stopped the major leak. Unfortunately the damage done was the line to the hot water heating boiler, so with this line shutoff the boiler had no water supply.

Called a plumber and he quickly replace the section of damaged pipe, but unfortunately the backflow in series to the boiler was damaged. He temporarily took off the backflow and replaced with pipe so the boiler would still have a water supply.

So my questions are:

1) plumber said the backflow is only a precaution if the water pressure from boiler is so great that it pushes back, but said this is really rare and thus removal temporarily should not be a problem??? Can someone comment on this??? He also said most hydronic boiler use glycol or some type of green chemical, and said that it would be obvious if the boiler pushed water into my potable supply as the water from taps would be green - again comments please???

2) plumber also said that the boiler uses constant water circulation and thus really does not need a water supply line to be kept on. He said if I was concerned due to no backflow to just turn off the water supply (the same shutoff valve I originally used) and that the boiler would be fine as it is already full with all the water it needs. Again need comments on this???

I do plan to replace the backflow, but need to know how urgent it is, and in the meantime do I turn off the water supply to the boiler or if boiler absolutely needs a constant water supply what are the odds of contaminating my potable ater.


yuri 12-11-2010 12:56 PM

25 yrs ago backflow preventors did not exist and we all survived. They are required by code and you should have one. The only time boiler water would get into the city water supply is if you lost all the water pressure due to a water main break and it siphoned backwards which is very rare. They need them on cooling towers on roofs of commercial jobs as they are a lot higher than the street and can easily siphon backwards. There is no large green amounts of water so you won't notice it. Your boiler should not require constant filling unless it or some pipes are leaking. Once filled you can shut off the supply BUT THIS MAY BE DANGEROUS if the boiler runs dry from a leak or lack of water. Cannot tell if it is safe from here. Your plumber should be able to cool down the boiler and pressure test the system for leaks/integrity. May require an air compressor and rigging to the boiler. Don't go higher than the relief valve setting on the boiler.

DanDaMan 12-11-2010 01:36 PM

Yuri - thanks for the quick reply.

Since my post I learned that my boiler is an open system and does not use glycol - thus I guess worst case scenario if I leave water supply on is a little "old" water getting into the potable supply. As you said, 25+ years ago backflows did not exist so I suspect even if it occurs that is not the end of the world.

However I was also told that if I leave the water supply on, that when I turn a tap on it will suck water and it could suck water from the boiler - thus that suggests drinking my boiler water could be a greater chance than your scenario of just when the main water supply were to leak or break. Comments??

Last question. I current have a Watts 009QT 1/2" backflow - it is quite a big unit with 4 'somethings' on the top which are not connected to anything. Plumber said these 'somethings' are used to test the backflow. Do I need the same unit when I relace it?? Went on ebay and saw many smaller 1/2" backflows for real cheap - these smaller/cheaper ones do not have the 'somethings' on top but many have something referred to as a vent (perhaps the vent is used to test). Anyway, can I use any 1/2" backflow??? Just curious since I don't know why someone in the past put such a big unit (and expensive) if they could have gotten away with a cheapy.


yuri 12-11-2010 01:45 PM

Normally you have a backflow preventor and then a automatic fill valve (prv pressure regulator valve) set at 12 psig to fill the boiler if it loses water and pressure. Not sure what you have there w/o some pics. You don't leave the water supply open all the time as city pressure 60 psig or higher will overfill the system. The Prv is there to do that or you manually open a fill valve on older systems and fill the boiler and bleed the expansion tank etc. The cheaper backflow preventors can dump water everywhere if the city drops its pressure suddenly. I am not a Pro plumber and don't know what the code requires in your area but you should use the proper one for your area. The 4 thingys are for the plumber to test the valve but I have only seen those in commercial apps where by law they have to be tested once a year.
Look at his pics for what you should have:

DanDaMan 12-11-2010 02:06 PM

Yuri, yes I also have a smaller valve downstream of where the backflow was, which I know is a pressure regulator (this regulator also has an arrow so it can only point towards the boiler). Before this issue occurred, the water supply was always kept on to the backflow, then to the pressure valve and then to the boiler. I suspect the boiler then was able to accept new water when and if needed.

Since my setup appears as being the newer type that does not require manual filling, I assume I'm OK with just turning off the water supply until I get a new backflow. Just in case, I will turn on the water supply for 5 minutes daily just in case the boiler needs more water.

As for the backflow though, can I get a cheap $20 unit with one test valve, or do I need a bigger unit like the Watts 009QT I currently have. Will pictures help?


yuri 12-11-2010 02:12 PM

Depends on your Local plumbing code and not what you hear on the net. Local rules supersede the others. The cheaper smaller ones may not dump water fast enough to meet the code etc. Post your location and someone on the board may know your rules, we also have a plumbing forum linked at the top of our home page. Or look up your City plumbing inspection dept in the mechanical and engineering section of the Blue pages and ask them.

DanDaMan 12-11-2010 02:26 PM

I'm in Calgary - anyone know what the code requirements are for my replacement backflow? Thanks. I will also post in the plumbing section for more advice.

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