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9 kW Mini boiler reset problem

My 12 year old mini boiler in my radiant floor heat system has been shutting down after the 205 degree manual reset switch trips. The thermostat turns off the pump when the proper temp is reached, but the boiler keeps heating until the reset kicks it off. Then I don't have heat when the temp drops and it is called for by the thermostat. Is there a relay or switch I should be checking that should be turning the boiler off? The boiler is an EMB 9 kW. The dealer I got it from is no longer around, so I'm searching for a clue on where to start with this. Thanks for any suggestions.


  • icesailoricesailor Member Posts: 7,265

    If your 9 KW Mini Boiler is electric, it would seem to me that it is like a electric water heater. If the water temperature in a electric water heater reaches 180 degrees, there is a manual high temperature cut out switch that cuts out and must be manually reset. When it trips, you are supposed to figure out why. With electric water heaters, it is usually because a thermostat has stuck closed and won't shut off. So, when the tank overheats, it shuts down.

    With your 9 KW Mini Boiler, 203 degrees is probably the high limit safety trip out that must be re-set. It is also the time to check the other thermostats to find out which one is stuck closed.

    Thermostats being what they are on water heaters, 203 degrees sounds high and very close to making steam. A nice little bomb in the house. If you don't know how or don't have the equipment to figure it out, call a professional. It's cheaper than the damage from a exploding water heater from steam.
  • Charles JohnsonCharles Johnson Member Posts: 24
    Electric mini boiler

    The 160 limit is an operating limit and the 205 limit is manual reset. If it is tripping and you notice the elements on even when the pump shuts off, make sure pump is wired into the pump terminals in the boiler. If it is, then the relays that energize the elements might be sticking. This is a common problem on these boilers.
  • Big-DBig-D Member Posts: 21
    Solution to 9kW boler high limiting

    The solution to your problem is to change the circuit board. What happens is the relays that control power to the individual electric heating elements develop a magnetic pull/hold on the relay thus keeping it close and providing power to the heating element at all times until, poof high limit trip. The technician thinks to just reset the high limit and the problem is solved. However the high limit is doing what it should. That is until he gets a call from the frustrated homeowner that the boiler is not working again. The high limit most likely tripped once again. The technician replaces the high limit only to find he is knocking on his customers door AGAIN!. Replace the circuit board and your problem with nuisance high limiting will be in the rear view mirror. Good luck. We have these circuit boards and sell them to homeowners or contractors that number about 30-40 of these type of problems each year.
  • JDWhirleyJDWhirley Member Posts: 2
    EMB 9KW Mini Boiler not heating up

    I've tested elements (like a hot water heater) with multi-meter and they seem fine (12.5 ohms) and when powered up there is power to the heating elements.  Does anyone have any other ideas to try to figure this out?  If the control board was shot would there be power at the element connections?  Thanks for your time.
  • hot rodhot rod Member Posts: 7,011

    has the correct answer from my experience with these boilers. There is not much on the board that is repairable. I have sourced the triac relays locally. Usually when the relay fails the element does not get power. If it is powered all the time, it is probably the board as suggested above.

    Was it hit by a power surge, maybe a connection to a generator? has some tech support help available via phone or e-mail.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • JDWhirleyJDWhirley Member Posts: 2
    EMB 9KW Mini Boiler not heating up

    Thanks for your quick reply.  There was not a power surge issue.  All of the indicator lights are on and power does not seem to be the issue, but the boiler is not heating.  Any ideas?
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