radiant calls for heat but making steam for whole house

dmcs

Hi,

I have a single pipe steam system.  I recently  gutted my kitchen and mudroom and installed radiant loops using warmboard-R with porcelain tile floor.  The radiant system gets heat from a plate heat exchanger off the steam boiler (I also have a hot water baseboard for a sunroom off that same heat exchanger, although it is rarely used).  Usually the heat works fine.  But, if for some reason the mudroom is cold (e.g. when contractors are there and the door is constantly being opened, the radiant t-stat calls for heat and the boiler fires making steam for the whole house.  So, the rest of the house that has steam radiators gets way too hot.  I thought the boiler would stop firing after it gets to a certain temperature and only the pumps for the radiant system would run.  But, it *seems* that the boiler and pumps are either both on or both off.  My guess is that it is a problem with the way it is wired.   I'm sure I need to provide some more detail about my system set-up to diagnose the problem, but not sure what other info would be most relevant.  If anyone thinks they might be able to help with solutions, please let me know what details I should provide. Thanks!

JStar

Heat

Could be a control or limit issue. Could also be piped wrong, or a failed pump,.



Any pictures? Where are you located?

Tom_133

Tstat

Did you land both the steam tstat and the radiant tstat on the TT of the burner? I had a customer who did that and man it was warm in there when I showed up to change it. If you did, the boiler will make steam as long as the radiant tstat calls, you would need to install a separate aquastat to call the boiler that would come on and off with water temperature and not allow the boiler to get warm enough to make steam.

dmcs

Tstat

Thanks for the input!  The Tstats for the radiant loop and the zone on the baseboard go to a Taco 502.  The tstat for the rest of the house goes to the boiler.  I have not traced all of the wires in the boiler yet (think plate of spaghetti) and was hoping there was some other obvious explanation to avoid that.  There is an aquastat on the steam return. Where would the additional aquastat go?   The contractor who put in the radiant system is supposed to come this week to try to figure it out, but I was hoping to get some ideas so I can discuss intelligently with him.

dmcs

heat

I checked the piping and it follows the shop drawings and the pumps seem to be working fine.  I am just north of NYC.

Tom_133

where does the TT go

If there isn't an aquastat controlling the boiler on the hydronic heat side then the boiler will run like a steam boiler, but if the aquastat interrupts the call to the burner at 180 down to 160 then the boiler will not make steam.

dmcs

aquastat or disconnect line to boiler?

On the Taco 501, there is a line from 5 and 6 normally open back to the boiler, which I believe is what is causing the boiler to fire when the radiant tstat kicks in.  If I just disconnect that will that work, so that the pump would run but the boiler would not fire?  The downside seems to be if the tstat for the rest of the house does not call for steam for a while, the temparature of the water in the boiler could drop so low that it would not be adequate for the hydronic system.  How likely does it seems that that would happen? My *guess* is not very likely since they are set for the same temperature and the heat loss is comparable. Any other views or other downsides to this solution (unless I am mistaken and it is not really a solution at all!)?

Adding an aquastat on the hydronic side of the boiler definitely sounds like a better solution and I will probably work on that for next heating season.  For now, just trying to avoid having to manually shut off the boiler to keep from overheating.

Thanks!

Tom_133

You got it

You have a full grasp on it, if you disconnect 5 and 6 or the TT back to the boiler you won't be calling the boiler. If you install an aquastat in the loop out of the boiler it will come up and down as it should. Make sure that the aquastat is high enough in temp to protect your boiler from too low of return water temp. Another caution is if you are not running some sort of heat exchanger then make sure you dont have any iron products in the radiant zone, such as the pump or black iron fittings the water that comes out of the boiler has lots of air.

dmcs

Will the aquastat affect the steam side?

Thanks for the advice!  I do have a flat plate heat exchanger to keep the hydronic side clean and have a strainer.

So, the aquastat will keep the boiler from making steam just because the radiant thermostat is calling for heat, but it will still allow the boiler to make steam when the thermostat controlling the rest of the house is calling for steam?  I think I will need professional help to figure out how to wire that.

What happens to the boiler if the return water temp is too low? 

I have an aquastat already on the return for the steam, but truthfully I don't know why it is there.

Tom_133

Temps

You dont allow to cool of return water to protect the boiler from condensing.



You typically wire the Tstat to the burner so the burner will run for as long as the house tstat calls and the aquastat that is on the radiant loop will be wired into the burner and the circulator relay box 5 and 6. So when there is a call it powers the circulator, sends a call to the aquastat which will run the burner up to 180 and down to 160. I do suggest getting in a pro to help with the aquastat and wiring setup.