radiant floor "Heating Box" KD-HBO100 doesn't pull hot water

[viqx]

I'm not sure if this qualifies as an "appliance" per se, but maybe someone else has some experience with this unit or similar...

My house's heat is provided by a flow-activated Takagi tankless water heater, and regulated by a Heating Box model KD-HBO100.  (The manual for the unit is here.) Yesterday, the pump just stopped pulling hot water.  By that I mean that the thermostat still turns on the HB, and the pump in the HB still comes on, or at least makes noise like it comes on.  When I turned off the thermostate and turned it back on, I could hear the pex in the floor creak for a second as the flow started, so that seemed normal.  I thought maybe the pilot light had gone out (or I'd forgotten to pay the gas bill) but the hot water at the tap still worked fine, so I figured the problem was not with the heater itself.

I figured there must be a bubble in the line somehow but don't know how to safely check for that or purge the system... I looked at a few other posts about boilers and stuff and the average idiot's intuition about air in the lines seemed to be right about 15% of the time, so I figured I'd better check with some friendly experts before doing anything clever.

*update* I turned the thermostat off last night in case that there was a big bubble in the pump somehow, burning it up.  Today I turned the thermostat back on and nothing had changed, but when I went into the basement and turned the box itself off and back on, this time it _did_ start pulling hot water -- only now it's making a squealing noise when it runs.  This makes me thing air in the line again...?  If noise is ok, then I'm ok -- I can't hear the squeal from the living space -- but I don't want it to burn out.

Any koans out there about radiant floors, O sempais?

[Bobice]

Try www.heatinghelp.com there are alot of "wetheads" that are on there.

[telefunkenu47]

sumewhere on the return side close to the circulator inlet you should see a shutoff valve and a boiler drain valve respectively. you may also find it near the radiant manifold if you have one. look around and get back to me. happy hunting! what is your system pressure running at right now. should be around 1 to 1.5 bar or 12 to 18 psi. does your system have a hand feeder or a watts type automatic feeder? The pdf file did not download. perhaps yopu could submit it again.

[viqx]

There's a little drain valve just upstream of the pump (pump=circulator?) but there's not anything that's obviously a shutoff valve in particular.  I don't know what a feeder is?

There doesn't seem to be any place that shows the pressure in an obvious way. 

I got the pdf from http://www.heatingbox.com/product.html and then clicking on the "installation manual" link, under the HBO-100 side of the page.

[Bobice]

Thanks for the link. Give me a little time to digest the four manuals. Just getting old.

BTW a feeder is what is used to supply water to a system commonly steam and hot water (hydronics)

[telefunkenu47]

The bottom of page 7 tells me thar you need to install Webstone isolation/purge valves in order to flush the system. I would consult with a hydronic heat pro if you dont know what that means. way beyond my ability to explain that to you in this forum. good luck!

[viqx]

Thanks for pointing that out.  I know what it means I think, but I wouldn't do it myself.

But, if there's just a small amount of air in the system would I need to flush the whole thing just to get a bubble out?

[telefunkenu47]

It will keep water from flowing in the hydronic loops. Try to isolate each individual loop at the manifold and flush one loop at a time. there is a air vent located above the circulator i beleive, is the cap loose on it so that air can escape? also look into adding a Spirovent air eliminator to the system. I think they are great, and well worth the money on a closed loop system. Also is the circ pump itself airbound, and are you sure the impeller is actually turning. Sometimes they need a little help initially to get the impeller freed up, especially at season start up.Im thinking of the grundfos circs on the Baxi Luna.