High pressure question - residential application

[Deleted User]

I just checked my boiler readings and things seem a little off. The outside temperature is relatively mild today - 40 degrees F. My boiler pressure is reading 24 PSI. Water temp seems a little high as well - 140. I have had higher pressure readings in 0 degree weather, but I don't recall them this high in the 40 degree range.

System details:

-20+ year old Hydrotherm boiler
-Cold system at 12 PSI
-new compression tank and circulator last winter
-2 pipe hot water system
-30 PSI pressure relief valve

Also, as I was looking at the system tonight, I realized that the circulator is connected to the pipe coming out of the bottom of the radiator. Is this correct? I thought the hot water came out of the pipe on the top of the radiator, through the system and then returned into the bottom of the boiler. If that is true, is the circulator "pulling" water through rather than "pushing" it? Or do I have something wrong here?

Thanks for the help!

Timco

Typical (and somewhat incorrect) for circ to be on the return. See it all the time, and usually it heats fine. Should be on supply pumping away from expansion tank. If pressure is 12 cold, and 24 hot, expansion tank may be undersized. 140* water is actually cool, as 180* is a typical standard temp.

Tim

[Deleted User]

Timco...thanks for the input. However, I am really confused now.

The expansion tank size makes sense, however, looking at my piping is what is making me confused.

I am assuming several things - please let me know if these are wrong:

1) Cold return water comes into the boiler at the bottom
2) Boiler heats water and it rises into the system out of the top of the boiler.
3) On the radiators, the supply side is the side with the flow control valve...the water runs through the rad and out the other side.

In my system, the pipe coming out of the top of the boiler (which I thought was the supply), is actually the pipe leading to the return side of my rads.

Is something goofy here, or am I misunderstanding something?

Also, my expansion tank appears to be connected to the return line (bottom of the boiler) as well. That is, the pipe comes in from the rads, then the expansion tank, then the circulator, then into the bottom of the boiler.

If I am explaining this wrong, I can take a picture and post.

Also, you mentioned 180* for temp. Would the temp get that high if the outside temp is mild? I guess I thought of it like this (I'm making numbers up here, but the picture should be clear): If it is 40* outside, the boiler would only fire every 20 minutes. In addition, it would not need to fire for very long. If it is 0* outside (ie, more heat needed to maintain a 68* house), the boiler will fire more frequently and for longer duration. Thus, the water temp would be considerably higher. Is this correct?

Finally, my boiler has a high temp cutoff right around 165* or so. When it gets really cold - below 0* - the boiler ends up short cycling as the water temp builds and is cut off at the higher temp. Once the water cools a few degrees, it kicks back in again and starts the cycle over. This is usually accompanied by my pressure relief valve tripping and spitting out a few ounces of water. Should I raise the high temp setting and increase the size of my expansion tank?

Timco

It sounds like you are still 'pumping away' from the exp tank, so that is actually fine. Yes, the bottom tap is the ret, and top is supply. Should not matter about the water going in the opposite side as the rad valve. Installer must have accidentialy reversed the supply & return. Do you have a outdoor reset I take it? If so, then yes, warm day = 140* water, and 0* day =180* water. Aquastat just acts as a high limit. Too many variables to get into supply & return temps, and delta t. Boiler should run continueously until it either satisfies the heat call, or makes the temp of hot water the reset or aquastat lets it, and kills the burner while still circulating.

Tim

[Deleted User]

No outdoor reset on the system that I know of. I can't find any wiring for it. Although that is on my must have list when I replace the boiler.

Timco

If no reset, then boiler always makes the water temp the aquastat is set for. warmer day = short cycle, may not even reach temp aquastat is set for...cold day = boiler will get to temp aquastat is set for, and kill burner until water temp falls.