Help! Pressure reducing valve leaking when boiler hot

[bpirger]

Hi All:

I noticed my system pressure (radiant hydronic, Garn fired) was staying near 0 all the time. Also noticed my pressure relief valve appeared to be leaking. SO I drained the system (garn is on the other side of plate HX) and replaced the pressure relief. I also checked the expansion tank (diaphram) and it only had a few pounds of pressure, so I pumped it up to 12. Filled everything and the pressure sat at 12psi. Great! SO I turned things back on and brought in some heat from the Garn and all seemed great. Fired the Garn and when temps started to rise to 155 in the primary loop, the pressure reducing valve (not the pressure relief) started leaking a lot! Shut off the heat demands and when the temp drops, the valve stops leaking. Leak coming out from the top of the valve, around the nut under the plunger to do a "fast fill".

So with the fill today I ran quite a bit of water through the pressure reducing valve into the system.

First time I have ever had a problem with this in the past 10 year of operation.....

SO, is it just time to replace this valve? Should I also replace the expansion tank? It sounds "empty" with a knock on it....and it seemed like it was doing fine given the pressure guage.

Pressure guage sits a long ways from the tank and all, but everything is the same system, so presumably the pressure is also the same.

I can only assume it is this valve that is leaking for some reason...but only at higher temp. When it is leaking, pressure guage has dropped down to zero.....as if only temp related....but that doesn't make sense to me.

The joys of self maintained/installed systems!

 

[maple1]

Did you try taking it apart? I've had mine apart more than once and got a bunch of gunk out - mine wasn't filling when it should though. Kind of weird that a temp rise triggers it. Is there a valve between it & the system you can isolate it with? I've got my fresh-fill stuff valved off from both sides all the time, and usually just run a hose to a bottom boiler drain fitting when I need to add water - the one I have srewed onto the drain of my Wye strainer to be exact.

 

[bpirger]

No, there is no valve between the boiler system and the pressure reducer. There will be now. I bought a new reducer, but of course the attachment fittings are different. The original has a male thread on the domestic side. I though there was a "half union" type thing used, but when I took the old one off, I see the attachment is directly to the "face" of the reducer (milled flat) with a little wafer washer. The new one is 1/2" female on both sides. So, I guess I will have to go back to the baock feed preventer and start there going to the reducer with 1/2". I think I have what I need....just hope I can find a 1/2" 90 around! LOL. It will be comical if I can't find one of those. House is all aquapex though, so the 1/2" stuff is scarce.

Let's see how many hours it takes me to get it all together.

There is a valve between the domestic water and the boiler feeder...I always keep that off as well unless I want to feed water in. Now there will be one on the other side. If worse comes to worse, I can fill it through a boiler drain and get the right pressure tonight "by hand" and continue tomorrow. It's only 9:40, early. Good to be a night owl sometimes.

Do folks see these pressure reducers fail often? Plumber I bumped into said 10 years is good these days...
Thanks!

 

[bpirger]

It took about three hours. Something is still different....I'm not sure. Operation for 10 years was rock solid, and now suddenly there is some oddities. One thing I see for sure that is odd is that heating DHW is now much slower than before. Since everything worked so well before, I never stopped and thought about a few things. I have primary/secondary setup with the DHW as a secondary loop with a pump. My primary pump is a 007 and the DHW pump is an 010. I figure the head of my megastor is about 3 ft. and the piping is about 25' of 1". The 010 moves a huge amount of water and I am certain I am setting up a reverse flow in the shared piping, essentially sending the same water through the megastor repeatedly. Hence, the DHW takes forever to heat, though it never did before. It is almost as if the primary pump (007) has lost much of its ability to move water, the 010 has suddenly started pushing what it always should have, or something else is amiss.

If I largely shut the ball valves on the 010 secondary loop I get hotter water circulating through the megastore, becuase I am not "mixing" it with that which just circulated through the megastor.

I can readily change this pump to something smaller, or perhaps swap it with the primary 007.

But why the sudden change? That is what I find so odd.

Everything is 10 years old....the primary runs constantly during the heating season, so it has many hours on it. Do pumps tend to die slowly?

When I drained the system today, the water was quite clear. I drained at the lowest possible point in the system...didn't see any chunks, crud, etc.

If I ever got that temp sensor monitoring system up and running, I'd be able to easily see when this transition all occured. I wish there was more time in a day.

 

[Fred61]

There is one element in domestic water heating that is not present in boiler water heating and that is calcium build up from constantly renewing water into the circuit. Components such as check valves, heat exchangers and mixers will calcify up and give you headaches like you're experiencing now. I don't know what components are in your system but it sounds to me like you have a sticking check valve.

I ended up installing a water softener due to calcification of components in my DHW loop.

 

[bpirger]

Fred, you refer to build up of gunk inside the fresh water side of the DHW tank? My DHW is a megastor indirect fired tank. So the boiler water passes through the HX inside the tank. Sure, the tank will accumulate all the build up from the fresh water flow, and that will impact for sure heating the hot water. But what I am seeing now is that flow through the DHW HX from the boiler secondary loop itself is altered. I do have check valves in that secondary loop external to the DHW coil inside the megastor (to make sure heat doesn't migrate out of the tank)...and a failure in one of these would indeed cause this type of problem....but then the secondary flow would be near zero....which I think means the primary loop would be circulating just fine without the reverse flow.

Or am I missing what you are saying Fred?

 

[Fred61]

I may not be getting the total picture of your set-up and your last post confused a little more. With that said, just remember that check valves will not only freeze closed but partially open caused by minerals on the seats or totally open or anywhere in between. I can tell you have a "good head" so with that in mind go back over your flow map and do some "what-if's". If you can shut off a valve and flow appears to get hotter, look upstream to see if you have a check valve that could be leaking by, causing reverse flow.

Sorry I can't be of more help but I'm just passing along some experiences I had with my DHW . You're not talking with a rocket scientist here!

How big (volume wise) is your secondary loop?

 

[bpirger]

Well, as a follow up....... If it seems that a good working system all of a sudden starts to act weird, reboot, right? Well, in this case, it is more or less the same! The Tekmar controller has many options for all sorts of things....temperature controls, setpoints, pumps/valves, etc. One of the options was changed, unbeknownst to me, and I didn't catch it. So, when I was trying to heat DHW, the DHW pump came on (secondary loop off primary), but the primary pump was shutting off! ARGH. My fault all the way, I should have known this by ear, but that damned DHW pump is a little bit loud. Anyways, after switching out a couple of pumps (I have more primary flow now...going to need it when I connect the new addition plumbing anyways) and I dropped the DHW pump flow down a bit (not enough though I think...I need a smaller pump...but I need to measure my drops across the DHW tank coil first to really verify)....I then realized the primary wasn't on when the DHW was. And I thought the 0015 was just so damned quiet! LMAO Gravity flow allowed some hot water to reach into the house (through a 40' 1" pex line burried) and now I know why that was as slow coming as it was!

It all makes sense now....and it was disturbing that such a change can come along all of a sudden like this without known cause. But as is usually the case, it was indeed a SOFTWARE problem. As a hardware guy, I know it 'ALWAYS' is.

And finally, the reason for a the change in settings. When the Garn gets down to 120 it is slow going to make DHW and sometimes the temp setpoint on the tank gets dropped down to prevent it from running forever trying to reach our 115 target (shuts off at 119). This is done through the Tekmar interface....and my wife accidently set one of the DHW mode settings wrong....and I didn't catch it. "My bad".