I have a Peerless 85 series hot water boiler (not sure of age). Several years ago (before we owned the house) the cast iron radiators were replaced with ¾ inch copper baseboard heaters with ½ inch pex running to them. We’ve had problems with the system ever since we moved in.

When the system is running, the pressure reading on side of boiler goes up to about 34 psi and the pressure relief valve drips/runs. I have a steel expansion tank mounted up between the floor joists which I purge quite often (more than weekly in the heating system). When I purge it expansion tank this stops the dripping at the relief valve (for a while), but then I get air bubbles in the system. Gradually over the course of a few days the bubbles go away but then the dripping at the relief valve starts again as the pressure builds up and I end up doing this all over again. The problem seems to be getting worse as I have to do this more and more frequently. Lately I have taken to shutting off the incoming water feed to prevent the pressure from gradually building but obviously this is not a permanent solution.

Is the pressure reducing valve on the incoming line bad (it says it’s set to 12psi with a range of 10-25)?

Do I need to replace the expansion tank?

Is there some other element of the system that controls pressure? I think the temperature might be too high too (210-220 F according to the pressure/temp gauge on the side).

 

I'm not sure why your expansion tank is getting waterlogged so often. When you drain it, do you drain it completely?

Do you have any open autovents on the system?

The dripping PRV is better than dripping pipes somewhere or an exploding boiler - it's doing its job.

Having the temp setting so high causes more expansion and that is making the whole situation worse.

I'd start by totally draining the expansion tank. Shut the boiler off, let it cool.

Isolate the expansion tank, and drain it until all the water is out. I used to have to cup my hand over a drain hose hanging from the tank and blow into it (you don't want to ingest boiler water) to force air in to break the air lock for getting the last of the water out.

Once all the air is out leave the isolation tank closed and slowly bump the pressure up to maybe 25 pounds and then run around and bleed everything you can and if there are any autovents close them.

Then super slowly open the isolation valve to the expansion tank.

I ended up chucking mine and installing a bladder type tank in its place and put an autovent on a riser and never had further issues for 3 or 4 years until I had the a new boiler installed - kept the bladder expansion tank.

 

As Who said, make sure you really are draining ALL of the water out. Think of a straw in a glass of pop. Put your finger over the end of the straw and lift it out. Pop stays in the straw. Same thing happens with the expansion tank, so you need to do something to break the vacuum that's created and holding the rest of the water in the tank. If you don't fancy blowing in the end of the hose, you can try closing the drain valve, disconnecting the hose and draining the hose, reconnect the hose and open the drain valve again. You may have to do this a number of times to get all the water out. If you have a small air compressor, you can blow air in the end of the hose too, and save your lungs.

Is the drain on the tank a standard drain ? There are some that are designed to break that vacuum... it may say "Drain-o-vent" on the valve ... If you have one of these, you may actually be draining the tank completely and not have to resort to the above measures.

Now... if closing the fill line to the boiler seems to keep the pressure under control, then I would say YES, it is likely that your auto fill valve (pressure reducing valve) is leaking and slowly increasing the pressure. If this is the case, have that replaced first, before doing anything with the tank.

Is your domestic hot water supplied by a coil in the boiler ? If so, this is another often overlooked reason for pressure buildup in a boiler. If that coil is leaking inside the boiler, it will slowly pressurize it until the relief valve opens.

I don't think PEX tubing is real happy with water that hot ! Turn the aquastat setting down to like 180*F or so...

 

Drained the expansion tank completely. As luck would have it, I do have a "drain-o-vent" type faucet. Also dropped the temp down to about 180*F. Method described by Who worked well and I didn't get any air in the system this time but... after starting at 15psi cold the pressure went up to about 35 and the pressure relief valve started dripping. I think I may try replacing the auto fill valve tomorrow.

As for the aquastat that's another problem. It's already set as low as it will go (140*F). A couple of years ago I had a plumber look at it and he installed a backup shutoff for the boiler that is strapped on to the pipe coming out of the boiler. I used the setting on this to lower the temp of the boiler. Should I have the aquastat replaced?

 

By all means have it replaced. Honeywell makes a nice electronic aquastat.

 

And this only happens when the fill valve is open ? If you shut the valve pressure stays under control ?

I would. The auxiliary high limit that he installed is really intended as a safety measure to protect in case of aquastat failure. To rely on that for normal day to day operation is probably not wise.

Yeah, what Grady just said (hi Grady!) I've got one on my list for Santa to bring me ... L7224 ...

 

Yeah, when I shut off the incoming line, the pressure stays under control.

 

Steve, before you condemn and replace the pressure reducing valve, make sure there's not a "fast fill" bypass around it that may be leaking.

If not, then it's pretty certain the reducing valve is leaking through.

 

No bypass, just the one line coming in. The pressure reducing valve has a fast fill lever on it too. Couldn't find a comparable one at Lowes. Guess i'll have to try a heating supply store during the week.

The Honeywell aquastat that was recommended, can that handle multiple zones? I just have one zone now, but there are three loops, each with its own circulator (two upstairs - one downstairs). Wouldn't having at least two zones, one upstairs and downstairs, be more efficient.

 

Steve, that aquastat I mentioned is the one that's on MY list for Santa ... not necessarily the one you need, sorry for any confusion there.

I tried to find info on your boiler but apparently Peerless doesn't have info on it's older systems on the website. Are you running oil or gas ? Can you find a number on the old aquastat ? Sometimes there's a label inside the cover, sometimes the number is stamped on the side panel inside, and sometimes it's stamped on the back (use a mirror).

You _can_ use another manufacturers reducing valve, chances are Lowes had the Watts unit (I think 1156 ?), at least that's what they carry around here anyway. Maybe you've got the B&G ... but either one will work. You may not have a backflow preventer installed if it's an older system. Now is the time to add one if you want to update it.

Sounds like you've got the biggest part of the zoning done already if your system has three circs. How are they controlled ? I'm guessing there must be a relay that runs them ? If you added a Taco zoned relay box and another thermostat or two you'd be in business. I don't know that it would save a lot though, heat loss is heat loss, and that's what you pay for. You might save a _little_ , by being able to run the less used areas of your home a bit cooler.

 

The R7224U is pretty much a fits all, at least for oil. Not sure if it works for gas. The burner output (B1 & B2) are 120 volts.
There may be a model for gas.

 

The reducing valve that's in there now is a Taco 329-3. I thought that it had a backflow preventer built in. That's the reason I didn't get the Watts model I saw at Lowes, because it called for a separate backlow preventer. If I replace it with an identical Taco valve do I still need to put in a backflow preventer?

The boiler I have is gas. The aquastat is a White-Rogers 8F48A-351. All three circulators are wired together and then to the circulator terminals. I definitely want to have this replaced and stop relying on the auxillary.

 

No, I don't see any reason for a separate backflow preventer, the Taco does have one built-in as you say.

I found the PDF file for your aquastat on the white-rodgers site, and it appears that there must be a honeywell unit that will replace it, but honey's cross-ref tool is coming up short... I know that they have one with the same functions, but whether or not it will fit the well in your boiler I can't tell.

still looking...

by the way, the 7224 is for oil only ...

 

A separate backflow preventer is now required my most codes but there are thousands of boilers out there without them. My advice is to install one.

 

Grady, that's even if there's one built-in to the reducing valve ?

It appears that the Honeywell L8148E is the closest match to your WR 8F48 ... (notice the similarity in the numbers? hmmm) ... but like I said, don't know if it will fit your well. It certainly is less expensive! The WR one from what I can tell is over $300 ... I bet the Honey one can be found for around $100 ...

Found it on WR website cross-ref ...
White-Rodgers Cross Ref

Patriot has it

 

Thanks for all the help.
I put in a new taco pressure reducing valve tonight and brought everything back up. After purging the lines the pressure seems to be holding at about 15 or so.

As for the taco reducing valve having a backflow preventer, that was my mistake. I thought that the "built-in check to prevent the emptying of the system if incoming pressure fails" was the same as a back flow preventer but I guess not, so I installed a separate one.

Now on to the problem with the aquastat. That Honeywell L8148E sure sounds (and looks) a lot like the White-Rogers I have in there now, right down to the terminal locations. Original boiler instuction manual even shows examples using both models. Is there any way to tell if it will fit my well, without taking the old one out?

 

I'd say that I'm about 99% sure it will be a direct plug'n'play replacement, you might be able to tell if you download the PDF for both of them and compare. I think I saw 'mechanical' drawings with dimensions in them.