Max E Therm 400 Fenwal issue

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D

Dodger

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Sep 17, 2017
649
Silicon Valley, CA
2016 heater installation. Main board stopped displaying anything, including on power up from breaker. Automation is Jandy Aqualink.

Heater display board is pre-2021, #42002-0007 rev D. No LED errors on back of board during power up. Confirmed 24 VAC coming to board, both on transformer output and on the yellow and yellow/white input to board.

LED above Fenwal box (35-662944-013) flashes once briefly on power up, indicating Air Flow Fault (correct?) There is no audible "tick" from air sensor and blower motor does not show any life at power up, so checked power to blower motor. Black/output from Fenwal F2 to blower motor measures zero. When the Fenwal is bypassed, power is restored and blower motor comes on with power up (tested only very briefly.)

Assume this means something (relay?) inside the Fenwal is bad. Is there something to debug inside the Fenwal, or just purchase and replace the whole box?

Or, is there some other possibility that needs investigation? No signs of chewed wires or clogged blower so far.

Thank you in advance.
 
Assuming that your heater is wired for 240V supply and looking at the Ladder Diagram on Pg 31 of this manual https://www.questargas.com/ForEmplo...ning/Boilers/Pentair_STA-RITE_MAX-E-THERM.pdf, in the idle ( no call for heat ) stage the heater you should have 240v between the F1 and F2 contacts on the Fenwal as L1 and F1 (the common terminal of the internal relay in the Fenwal) are connected and F2 ( the normally open contacts of the internal Fenwal relay ) is read the same as L2 through the motor windings since the circuit is open. When the heater calls for heat by applying 24V between IND and GND on the Fenwal through the WPS and limits the internal relay for F1/F2 contacts should close completing the circuit for the motor. If you read 240V between F1 and F2 with no call for heat and see 24V between IND and GND on a call for heat, but still read 240V between F1 and F2 on a call for heat then you have a problem with the internal Fenwal relay. This can be either that the relay is not closing or the contacts on the relay are bad. If this is the case, you should replace the Fenwal, but after replacing it would be a good idea to check the amp draw of the motor as overamperage could cause a deterioration of the relay contacts.
 
Thank you Allen.
And thank you @swamprat69 . Navigated slowly through your technical instruction (above my pay grade :unsure:.)

* Confirmed 240V between F1 and F2 lead with no heat call.
* Used automation to call for heat
* Surprised to see the heater display step through the expected messaging (188, 128, r13.)
* Surprised to see no flash on the Fenwal LED (not sure why this went away)
* Confirmed 24V between IND and GND.

Surprise. Blower fired up. Heater came on after usual 20sec delay and stayed on. Tested for ~10 minutes.
Basically, did no fix except a lot of disconnect/reconnect for measurement purposes, but it is suddenly working.

swamprat69 said:
check the amp draw of the motor as overamperage could cause a deterioration of the relay contacts.
Click to expand...

Is this something to be checked still? Forgot to do this before putting everything back together.
 
Most multimeters are able to read amperage (up tp 10A) when placed in series with a load (you don't need a clamp around ammeter for small loads). By removing the F1 wire and attaching one lead of the multimeter to the wire and attaching the second multimeter lead to the F2 terminal with the wire still attached and the multiimeter set to read amperage you will read the motor amperage when it is powered. Be sure to power off the heater when attaching the meter leads as both F1 and F2 have power when the heater is not calling for heat. Also be sure that bare meter lead contact points do not touch any grounding surface.
 
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