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Weil McLain ultra fault indirect Domestic hot water

HortHort Member Posts: 5
Recently I have noticed that during most calls for domestic indirect hot water heating that the return temperature is a few degrees hotter than the supply temperature and I get a lockout that automatically resets itself in time.
I have a post pump time set for 20 sec. but there does not seem to be a pre-pump time to set that may keep this from happening. This is DHW priority 1.
This is a recently new situation but has occurred during the heating season and now during warm weather shut down for house heat. Weil Mclain Ultra 105 series 3
Any thoughts?
Max supply 160.
mod on diff 2
mod off diff 10
Max rate 94%
Min rate 20%
Lockout usually occurs during first call for hot water in early morning


  • EzzyTEzzyT Member Posts: 985
    Sounds like you have a flow issue. Check the circulator that it’s running and if so make sure there isn’t any debris stuck on the impeller.
    Creative Solutions Plumbing & Heating LLC
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  • Tom_133Tom_133 Member Posts: 687
    It may also be one a faulty supply or return sensor, perhaps its seeing a temperature differential that is too large but its not real. Test the sensors with an ohms sensor.
    Montpelier Vt
  • HortHort Member Posts: 5
    Thank you both for your response and I will check both. To test the sensors is it best to test both at freezing and boiling?
    With the circulator can I disassemble the circulator and use the same gaskets when putting it back together?
    I am getting ready to do the annual cleaning so it is good timing to do all at the same time.
  • Tom_133Tom_133 Member Posts: 687
    you can test the sensors in place, look at what the control is saying for the temp then remove wires and test. The ohms scale is in the manual and it should be pretty close.
    Montpelier Vt
  • unclejohnunclejohn Member Posts: 1,545
    Is the indirect on a zone valve. If it is the post purge on the pump won't do anything.
  • Tim_DTim_D Member Posts: 34
    Check your high limit setting in the boiler settings menu. It should be at 200f. Then go to the system settings and go to priority 1. Go to temperatures and ensure that the target temp is 175 with a 5f on and off differential. I the DHW piped off of the boiler or off of the header? Be sure that the DHW direct or DHW system selection matches the piping.
  • HortHort Member Posts: 5
    Thanks uncle john!!! No zone valve
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