Purge air from radiant heating system

jayanderson

Hi folks,
I've got a question about bleeding the air from a radiant heating system. It's a fairly simple system, with only one zone heating my basement. When I turned it on this fall, the pressure relief valve on the water heater was leaking, so I replaced the valve and the expansion tank. The system is not leaking anymore, but I've introduced a lot of air into the system. You can hear the gurgling and also see the air bubbles passing through the lines. What's the proper procedure to bleed this system? Thanks in advance for any help.

jinbtown

Above the gray expansion tank is the air separator. Make sure the little "valve stem cap" is unscrewed a couple turns, you'll hear air hiss when you open it and then it should hiss every once in a while as air collects and then purges. Leave the Taco circulator pump running for 10-20 minutes at least. Air will purge automatically. When it's all quiet, tighten the little valve stemp cap thingy back down to seal it. Good to go.

psb75

Purge your system well using the left-hand blue rotary boiler drain with the yellow ball-valve closed. Put a short hose on the boiler drain and put end into a bucket. With circ. running and fill-valve open, and boiler drain valve w hose open, purge air out into the bucket. When you get straight water stream with no more air (bubbles in bucket) the radiant system has been purged. Looks like you are using a water heater as heat source. Not the best choice. Also is your circulator "in front" of your X-tank? If yes, also not good.

jayanderson

psb75 said:

Purge your system well using the left-hand blue rotary boiler drain with the yellow ball-valve closed. Put a short hose on the boiler drain and put end into a bucket. With circ. running and fill-valve open, and boiler drain valve w hose open, purge air out into the bucket. When you get straight water stream with no more air (bubbles in bucket) the radiant system has been purged. Looks like you are using a water heater as heat source. Not the best choice. Also is your circulator "in front" of your X-tank? If yes, also not good.

Thanks for the information. Yes, the system is heated by a water heater, which I agree is not the best choice, but it's what the previous homeowner had installed. I plan to replace it with a proper boiler in a few years. The water flow goes from the expansion tank to the circulator to the water heater, so I'm thinking the circulator is 'in front.'

Which valve do you consider to be the fill-valve? I'm assuming that the lower-left blue rotary valve is the drain valve. Thanks for your help, this is the first time I've ever done any work on a radiant system, and I'm glad to be learning about how my system works.

STEVEusaPA

jinbtown said:

Above the gray expansion tank is the air separator. Make sure the little "valve stem cap" is unscrewed a couple turns, you'll hear air hiss when you open it and then it should hiss every once in a while as air collects and then purges. Leave the Taco circulator pump running for 10-20 minutes at least. Air will purge automatically. When it's all quiet, tighten the little valve stemp cap thingy back down to seal it. Good to go.

You might want to take a look again at the picture before giving the wrong advice.
There's no cap, different air eliminator.

@OP It looks like 2 zones, or 1 zone and an indirect. Are there zone valves?
Can you show a picture showing the entire near boiler piping, the boiler and where water is added to the system?
How much pressure in the system?
The relief valve leaking may not have been from just a bad expansion tank.
Also, do you have access to a utility sink? The best purging will be done with a hose, in a 5 gallon bucket, in a sink.

jinbtown

Whoops, that's my bad, didn't zoom in on the computer. OP don't listen to me haha.

AdamInEvergreen

"The water flow goes from the expansion tank to the circulator to the water heater, so I'm thinking the circulator is 'in front.' "

If the flow is going as you say (Expansion tank -> Pump -> water heater) then you are "pumping away"  from the expansion tank, which is good.  @psb75 was concerned the flow went the other way (water heater -> pump -> ex tank) which would be bad.  Pumping towards your expansion tank can cause air issues

I'm interested to see how you answer STEVE's questions.  Along the same lines; is this tank providing domestic hot water for your house?

jayanderson

Thanks everybody for your comments and help. No, this water heater tank does not provide domestic hot water for the house. Their is a totally separate water heater for that, and the two tanks are not connected in any way. I didn't own the house when this was installed, but I'm assuming a water heater was used because it is such a small system.

I've attached a another picture of the system. Thanks for the help!

jayanderson

Also, there is no connection to an automatic water filling device on the system. Since I've owned the house, I've never added any additional water to the system. But after changing the pressure relief valve and the expansion tank, it was obvious that air is in the system.

AJCimino

If there is no fill line for the system you have to provide one. You let out water and did not replace it as I surmise from your post, so you have to add water to get back to where you were. Is there any pressure in the system? You can add water through the boiler drain on the return closest to the heater. Attach a washing machine hose to that boiler drain and the connect it to a hose bibb with your garden hose. Close the ball valve in between the boiler drains and open the other boiler drain and introduce water, purging the air from the system. Another issue you may have is that your two heating zones do not have isolation valves that I can see, so you will be purging the two zones at once. The one with the least resistance will purge and the other one probably won't. A ball valve should be installed on each zone so that you can purge one zone at a time.

STEVEusaPA

What brand water heater. Most aren't certified to be used for radiant heating.
You didn't answer my question about 2 zones/zone valves, or is each branch its own loop.
And also do you have a laundry sink.

jayanderson

STEVEusaPA said:

What brand water heater. Most aren't certified to be used for radiant heating.
You didn't answer my question about 2 zones/zone valves, or is each branch its own loop.
And also do you have a laundry sink.

I got the system purged. All is running well and is completely quiet. Pressure is holding steady around 15, which is probably a little high, so I'm going to lower it to 12 if it doesn't settle there on its own in awhile. Water heater is a Richmond, BTW, but I don't plan on using it for much longer. It's obviously louder than a boiler, so I plan on replacing it fairly soon. Thanks for the help!

jayanderson

I connected a hose to the upper right purge valve and a water supply to the lower left valve. Put new water in the system while the upper right purge was open. The water coming out of the hose spit a lot and it was obvious that there was lots of air. But it's all out and is working great. Thanks!

AdamInEvergreen

Great it worked for you. If it comes back try submerging the end of the outlet hose in a bucket while draining as it will give you a much better idea if there are any bubbles coming out. If that doesn't work you'll need to isolate each loop by installing new ball valves or manipulating zone valves (if they exist...). 

Verify the PEX is oxygen barrier before you put a new boiler in there.