Problem with a hydronic loop on a steam system

jorsch

I have a one-pipe steam system that heats the main part of my house. There is a separate room that is heated with hot water baseboards that tap water off the steam boiler. (There is not an isolated loop with a heat exchanger, it is taking water directly from the boiler. I know this is most likely not proper, but it's what I got when I bought the house 8 years ago.) Lately I have been having a problem with the hydronic loop. It has a separate thermostat, and it appears to be working because it will switch on the circulator pump. But it will not fire the boiler to generate hot water. The only way I can get heat into that room is to crank up the other thermostat on the steam side to make the boiler fire, but then I get the rest of the house too hot.

I've been looking at this for the last several days but I don't know how to troubleshoot it. There is a Honeywell R8845U which seems to be what controls the hydronic loop. There is a a Honewell L6006C aquastat to measure the water temp in the outgoing leg of the hot water piping. It's set to 190 with a differential of 5. (I don't understand what the differential does). The R8845U seems to be working because both LEDs (Heat Call and Relay) light up when the thermostat is calling for heat:



I'm at the end of my rope, because I don't know what to do to try and fix this. I consider myself handy but I don't know about these electrical controls.



Any advice or help would be appreciated.Thank you!

Jordan

JStar

Pump

Sounds like a control issue. The relay should have a set of contacts that turn the boiler on. The aquastat will stop the boiler from making steam if only the pumped loop is calling for heat.



The green TACO circulator is incorrect for this applicaiton. You need a bronze, air-cooled circulator. Have you had to change the pump since living in the house? My guess is yes.



I see a copper pipe on the steam supply. This is also incorrect. The copper will slowly deteriorte all of the iron in the boiler and destroy it from the inside out.

nicholas bonham-carter

Even worse

The steam is being accelerated by a reduction of riser pipe diameter as it leaves the boiler, which most likely is shooting up a lot of boiler water with it. Do you have any water-hammer present in the system?

It's time for an examination of your whole system, in order to reduce your fuel consumption/carbon footprint.--NBC

Si_zim

Check aquastat

If you can test the aquastat that would be a good first step. When the system is cool (and/or switched off for safety) take the cover off the aquastat and check continuity between the terminals. Blow it out also in case there is dust etc gumming things up. I can hear my aquastat click in as the water hits the main setting temperature and back out after the differential - not sure if you can discern this with other noises going on in the system.

After you check the aquastat - maybe move on to checking the relay wiring. You may want a larger differential to prevent short cycles on the hydronic heat... lower the main setting if you start getting steam popping in the hydronic zone. Or if you dont have one - get a bypass put in to prevent steam. This was the biggest improvement to my system which is similar to yours. http://documentlibrary.xylemappliedwater.com/files/documents/2011/06/CounterPointJun04-B.pdf

Ours was done with a flow control valve on the outbound after the circulator (to prevent heat when not being called for) and a ball valve on the return after the bypass branch so I can control the mixing of bypass/boiler water

Jordan Schwartz

Fixed!

Jstar and NBC - thanks for your comments. I know that the steam system has issues about the piping and the header, but I have to save those to be resolved for another day. Yes you're right about the Taco pump - I actually just had to replace it, after only ~4 years since the last replacement. Good to know but I figure I have time since I just put a new one in.



Jstar you comment about the aquastat got me thinking, and my wife did some Google searching, and let me to investigate it a bit. It turns out that it was connected incorrectly - it was set to cut in at a min temperature instead of cut off at a max. I rewired it and changed the differential and it seems to be working.



I came back to post and saw your response, Si_zim - thanks you were definitely right! And thanks for the link to that document - very good reference. It also calls for the bronze pump that Jstar mentioned.

Mike_C

I have a very similar set-up with a slightly different problem. The system is one-pipe steam in main part of house with hydronic loop taking water directly from the boiler. My problem is that when the loop side thermostat calls for heat, the boiler DOES go on, but the circulator doesn't and the boiler stays on endlessly a long as the loop side thermostat is calling for heat. Setup/controls are: Honeywell L6006 aquastat, Taco SR501 switching relay, and Taco 007-F5 circulator. (None have any visible crimped lines, scorching, or dust.) All three of these were replaced last year and the system did work throughout the New England winter until March.

Any guesses which control (or other aspect of system) may be failing? I could replace all three again but would love to try the most likely culprit first. (Previous suggestion above about the circulator not being right is noted, although I don't know why. And it would seem even with a bad circulator that the boiler should not have stayed on, suggesting something else.)

Am not desperate, but there are still some cool days and nights in late April here. Thanks very much in advance.