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I am using a takagi th-3 -p heater as a heat source for a…

Customer Question
I am using a...

I am using a takagi th-3 -p heater as a heat source for a radiant system. it is not heating, keeps shutting down.

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

I have a loop with a circulator and 3 radiant zones off the loop

Contractor's Assistant: Do you plan on doing the work yourself?

The flow is at 2.4 gal I am a heating installer. All three zones are calling for heat, all circulators are on. Why is the flow rate not higher? And why does it keep going to stand by?

Contractor's Assistant: Anything else we should know to help you best?

As long as flow is going through the th-3, shouldn't it be firing off?

Submitted: 7 months ago.Category: Plumbing
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Answered in 5 hours by:
12/3/2017
Plumber: Phil, Mechanical Engineer. replied 7 months ago
Phil
Phil, Mechanical Engineer.
Category: Plumbing
Satisfied Customers: 9,695
Experience: Retired mech. contractor, shop owner, 51 yrs experience.
Verified

Hello, if there is any air trapped (at the high points of the hot water loop or inside the floor coils) the system will be 'vapor locked' and not flow any water through the boiler and the boiler will go off when its high limit switch trips.

Venting the air is step number one.

.

My goal is to give you the best experience possible! I hope I have earned a 5 star rating! Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave today. If you need more assistance, please use the reply box and let me know.

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Customer reply replied 7 months ago
I am a heating professional, the obvious is not what I am having issues with. The heat source is a Takagi h-3 lp radiant heat unit. It is limiting the flow rate (which is what fires it off) in the circulation loop. When fist pluged in it runs at 1.9 gpm and decreses til it is under the required limit for ignition of .4 gpm. once the unit cycles once and shuts down it does not reignite even if flow rate is above the required .4 gpm
Plumber: Phil, Mechanical Engineer. replied 7 months ago

Thanks, ***** ***** thing we need to be sure of is that the differential on the flow switch is not to wide ... for instance, trips off at 0.4 gpm and does not come on until 1 gpm or whatever... you can test that by fitting a jumper across the flow switch for a few seconds only.... in order to see if bypassing the flow switch allows the boiler to fire or not.

If the boiler then fires we know it went off on the flow switch and the differential was too wide or the flow switch was sticking...

.

IF however the boiler does not fire then it is is quite likely that at low flow rates the boiler trips its high temperature cut out switch, will not reset unless you cycle power to the boiler to reset it. wait 10 or 20 minutes for the boiler to cool before attempting the soft reset.

Let me know how all that goes, we can proceed from there without any time limits

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