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[Corngrinder]

Fired up the OWB today...

I cannot, for the life of me, get hot water from the OWB into my DHW HX, nor can I get it into my Water -> Air HX.

This is my 3rd season using the OWB (Central Boiler 5036).  I did all the plumbing and installation myself.  It's a very simplistic set-up and I'm very familiar with it.  Water exits the boiler via a Taco pump, runs underground through my Thermopex, enters the house, comes through my Thermostatic Mixing Valve, enters a plate HX for DHW first, continues into my furnace plenum via a water -> air HX, then exits the house through the aforementioned mixing valve. Basically, everything was installed to manufacturer recommendations.

Hot boiler water is making it to the mixing valve just fine.  At first, I figured my loop (past the mixing valve) was vapor locked since it is physically higher in elevation.  This is not the case, I have bled the line.  I've also purged both HXs using an external water supply (backflushed, if you will).

Furthermore, I can break my loop in multiple spots to verify flow. If I break my loop before the DHW HX, I get boiler water to come out.  If I break it after my DHW HX, I get the same result (proving to myself that the HX isn't plugged).  I can do the same thing for the water -> air HX with the same results.  Point being, neither HX is plugged.  This also proves that the mixing valve is working since boiler water will make it to the broken loops.

When I piece everything back together, however, I get the same problem - no flow to either HX.

I'm left with very few things to check:  Either my pump doesn't have enough a** to get water through the system effectively (although, it appears to have more than enough pressure when broken) or perhaps my mixing valve isn't working as well as I think it should? Or... am I completely missing something?

Does anyone have advice?  I'm getting a little desperate; burning propane isn't nearly as fun as wood (or as cheap).

I really don't want to start mindlessly replacing parts until I find a cure either...

[RSI]

Where is the pump located?
It sounds like the mixing valve has to be passing all the water through it.

[slimjim]

If the mixing valve is stuck in the open position, I think you would still be sending some water to the exchangers but at a very reduced flow and your heat would be returning to the boiler, I think I would start there.

[Roger2561]

I know it may be a little work but is there a way to temporarily by-pass the thermostatic mixing valve?  If you're still not getting hot water at the HX, at least you've narrowed the possibilities...   Roger

[Pointblank]

What temp do you have your stove set to? The bypass valve needs 170 degree water to be fully open. At 150-170 its only partially open and anything under 150 its closed. If your water is up to temp, maybe the valve is stuck in bypass?

[Corngrinder]

My boiler temp was roughly 190 when I made the post.

Also, since posting I came up with a few more clues... and I reckon they point towards a stuck Thermostatic valve, but don't let my opinion sway yours.

Here's what I got:
The plumbing after the mixing valve heated up overnight.  It's what I would consider "average temp" from what I've observed in the past.  I noticed this for a brief moment last night as well, however it was after I had purged and bypassed the HXs, so I didn't put much into it. When I use that heat (via turning on the furnace or using DHW) the little heat that was "stored" dissipates and returns to ambient room temp.

This is what I observed only by touching the pipes and trying to utilize the heat.

To answer other questions:
No, I cannot bypass the mixing valve (unless I run about 75' of temporary hose).

The pump is located about 10" away from the discharge port of the boiler, inside the utility door or the boiler.


Also, anyone familiar with the innards of a Central Boiler Thermostatic Valve?  Is this something I can take apart and fiddle with, or does it need to be replaced if that's the problem?

[Pointblank]

IIRC, there's a thermostat in there similar to the one in your car. The valve splits in half by removing the 4 bolts. Im thinking you can pull the thermostat out, bolt it back together, and run without it. Remember which way it sits in there so when you get a new one you won't put it in backwards.

[Corngrinder]

Roger that.  I'm almost 100% confident that it is indeed the Thermostatic Valve.  When I take the HXs out-of-line, they heat up within about 5 minutes.  Once I put demand on them, they cannot keep up.  All the while, the heat at the mixing valve remains constant.

Is there more than 1 regulator inside the mixing valve?  And if so, do you reckon it's the valve that allows the OWB to recycle that is stuck open, or do you think the valve that allows heated water to my HXs is stuck shut?

Thanks for all the advice.

[Pointblank]

OK, just went out and looked at the one in my garage. It does in fact split in two, and the thermostat is right there. When its closed, the water gets redirected to the stove, when open, it flows out toward the heat ex. Only problem is there's an o ring on the thermostat that seals the 2 halves together, similar to what seals your pump to the pump flange out on the stove.  Remove the tstat, and there's nothing to seal the 2 halves together.

You could maybe pull the oring off the tstat and reuse it to make the seal. Or you might get lucky and there's something obstructing it and can just clean and reassemble.

[Corngrinder]

Definitely looks likes my T-stat is busted.  The gasket is worn as well. I might be up sh*t creek until I can get a replacement.  Going to see if an auto store has a gasket of similar size. 

I'd attach pictures, but my internet is too slow to upload 

[fireboss]

You can run with out it I have the 6048 same stove just bigger and I don't have one! You can get a  t stat next week ! Just cut old one out and put coupling with hose clamps!

[Corngrinder]

That is my plan.  Going to go see what  I can come up with gasket-wise... then put it back together and order one.  I really don't wan't to bypass it; seems it would be easier to fix it than do all that new plumbing.

[fireboss]

Put some permatex  that what you would use in a car t stat!

[Corngrinder]

Well...

I got a new gasket from AutoZone (Acura T-stat gaskets are just about perfect in size).  The gasket has been replaced and I removed the T-stat from the mixing valve.  Woohoo.... problem solved, right?

Nope.  I got no flow past the T-stat still.  What is going on?

[fireboss]

Maybe air bound?