Drain,Fill, Upgrade?

Old 12-13-05, 10:51 PM
Visiting Guest
Posts: n/a
Drain,Fill, Upgrade?

First off, great forum, I have learned many things here and am hoping to learn a little more.
So here is my problem. I have a leaking water supply valve on my Peerless (circa 1975) model MMW-145-WC gas boiler. This is causing the pressure to drop in my boiler and I think is the reason we have minimal heat at the radiators. See picture link for details on configuration. It is one zone with one circulator pump. So I have a couple questions:
1. I was planning on opening the top floor radiator bleed valves and draining the water from the hose bib on the boiler. I assume that is the correct way to do it?
2. Is there a particular order to refilling the system?
3. How do I check the expansion tank to see if it is working correctly?
4. Is there an additive I should add to the system? I could pour it into the boiler supply pipe before installing the new valve.
5. Should I add some sort of auto bleed valve on the pipe?
6. Any other maintenance I should do while I have the system down?

I replaced the thermocouple 2 days ago and noticed the pressure was low (around 10psi). When I added water to bring it up (to about 18psi), the valve must have started leaking. It now drips constantly.


Water Supply, Thermal tank, Radiator supply line
Old 12-14-05, 05:51 AM
fixitron's Avatar
Join Date: Dec 2005
Location: Warren, Vermont
Posts: 327
Upvotes: 0
Received 0 Upvotes on 0 Posts
From the picture, it looks like you have to manually feed the boiler by opening a valve. Is the water is leaking around the stem of the valve? If so, take a wrench and tighten the nut on the valve stem, where the stem comes out of the body. Do not overtighten. Check that you can still turn the valve after tightening.
A cold boiler should have a water pressure of about 12 psi. If you put the pressure up to 18 psi, the relief valve may lift (@ 30 psi) when the boiler water gets very hot, if the expansion tank cannot handle the amount of expansion.
Why do you want to drain the system? It will add air to the system and add to corrosion, loosen up crap that has settled in the piping and can create associated problems.
The consensus of heating professionals that I work with, for most applications. is to not add any treatment to the water in a heating system, that includes anti-freeze.
Tap on the expansion tank with a wrench or something solid. It should sound dull at the end attached to the piping (water end), and have a ring to it on the other end (air end). If it is dull throughout, it is water logged and should be replaced. Also check the "pre-charge" pressure on it. With the pressure on the water side at 0 psi, the air side should read 12 psi.
An aouto bleed valve only helps if there is an air scoop, which is a device put in the piping to physically knock air out of the water. A bleed valve on top of it allows the air to escape. An auto bleed valve at the high point(s) in the system could help.
My top maintenance check is to check for proper venting. Make sure that the boiler vent piping is still connected properly to the chimney and is in good condition, especially at joints and the bottom of the pipe.
If you can see the flames without taking the boiler apart, make sure that they are a nice even blue flame over all burner tubes. If not, have your heating professional check it out.
You should make sure that you have at least one operating CO detector, preferably one on each level of the house.
Old 12-14-05, 06:48 AM
Visiting Guest
Posts: n/a
I do have to let water in manually. Water is leaking from the stem of the valve. I believe the washer is shot. I attempted to tighten the nut, but the deposit build-up from our hard water has locked it in place.

The expansion tank makes a dull sound all the way to the top.

I would certainly like to avoid draining the system if possible but there is not a shutoff between the expansion tank and the boiler supply line. If I had to remplace the tank, I would add one. If I have to drain the system to fix the valve and tank issue, could I add the air-scoop into the horizontal piping in shown in the picture? Thanks.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: