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A difficult Heatmaker service call

Ken C.Ken C. Member Posts: 267
Had a customer this morning with a Heatmaker HW-M2 (Mark II). They had hot water, but poor heat from their baseboard. There was no voltage going to their circulator (the one outside the boiler, not the one inside the boiler). After quite a bit of tracing wires and using my VOM, I suspected a bad low limit.
The Heatmaker low limit is basically a strap-on style aquastat with three wires. Two wires go to the board, and if I jumped those out, the burner would come on. The third wire goes to a relay, which activates the external circulator. I could only get voltage at the circulator by jumping all three wires together.
I replaced the low limit switch, but still no voltage at the external circulator. I thought that maybe the new switch was defective, so I tried a second new switch. This time, the burner came on, but still no voltage to the external circulator.
This doesn't make sense. I got voltage to the circulator when I bypassed the low limit, so that would indicate a bad low limit. But what are the odds that two new replacement parts are bad?
I considered the possibility that the board might be bad, but the replacement board that came with the service parts kit for the Heatmaker had a connector for the secondary that didn't fit with the connector from the transformer. Therefore, I didn't get to rule out a possible bad board.
Long story short, I failed to get the heat back on.
Was there anything else I should have checked in my effort to find out why no voltage was getting to the external circulator? Or did I just use the wrong method to check the limit switch (especially since I'm used to a 2-wire limit switch)? The service manual for the Heatmaker is not that easy to follow, in my opinion. I'm stumped!


  • WeezboWeezbo Member Posts: 6,232
    try this..............

    plug the outside recirc on full time (into an extention cord. now supposedly if the pump is a problem it wont go. if it goes....great. if not exchange the cartridge. the low limit switch is a strap on .so make sure everythings snug on the pipe and wrap something around thpipe and lower half of the control....take a screw driver and turn the low limit up and down and listen for a Click......if it clicks at 70F and the pipe is justabout burning your hand off.........there are two likely reasons one is it isnt making good contact or its broke.the small capilarry tube doesnt take too much abuse...........if it does click off and on around 100 or 140F or whatever then test the leads to the pump from the limit switch if it doesnt read 120V its toast.Or it isnt powered on the line side. if it has power to it then the capilliary tube is toast.meanwhile the circ is running and theplace is getting warm..........some times they have some relay ahead of mayalso be fuse protected,isolated by or from other controls due to amp loads and the like. however i go with the easy and progress to the level of mystery :)
  • Ken, that low limit switch is

    SPDT switch. Once the low limit reaches temperature it will make the N.O. contact bringing in relay R1 which is 24 volts. This brings in 1R1 relay contact which feeds 24 volts to operating control which provides 24 volts to the module. This in turn closes 2R1 which is wired to 120 volts which powers the external circulator.

    Are you allowing the system to warm up and satisfy the low limit? If not the circulator will not come on until that switch walks over.

    You have to be careful as there was a wiring change to some of these. Do you have all of the factory bulletins? Without all the factory bulletins you will never be able to properly service Heatmakers. They had many changes and several different modules used depending on the model of the Heatmaker.

    I offer a three day course on these if your company is interested.

    I guess you must have gotten your liscense as you are servicing gas equipment now. Congratulations
    I assume if you have the Heatmaker parts kit you have had the factory training. Is that correct?
  • Ken do not try to adjust

    that low limit control as it is factory set and if you turn the adjustment screw you will screw it up.
  • WeezboWeezbo Member Posts: 6,232
    Thanks Tim...whews..*~/:)

    if the relay isnt seeing 24 v then there must be a reason ahead of it....either someting isnt making or there is no power to a transformer....sounds to me like the ken will be checking quite a few things tomorrow. Better go with not dialing on the temp screw then Ken.the fact that it makes when you (spun )connected the wires means that it wasnt getting the message to "Make".that you in deed have line voltage to the pump just no message to that controler.
  • Ken C.Ken C. Member Posts: 267
    Hi Tim,

    At what temperature does the low limit switch make and send voltage to the circulator? From reading the manual, I though it was 155 degrees, but my boss said the boiler has to reach 190 degrees before the circulator comes on.

    I noticed that the service parts kit does contain an awful lot of service bulletins, leading me to believe that these units are trouble-prone. As far as different boards, I asked the leading heating supplier about that, but they said the one I got was the only one they have available for the Mark 2.

    I would be interested in your Heatmaker course; can you e-mail me more information on it?

    As to the assumptions in the last paragraph of your post, the answers are no on both counts.
  • TonyTony Member Posts: 608
    low limit

    Is more than likely your problem. It's strapped onto the domestic HW outlet, so that's what needs to get to 160F. The gauge is reading the discharge of the boiler coil, a bit of disparity between the two. The gauge could very well read 190 before the DHW gets to 160. Your domestic coil could be coated up on the inside, slowing the heat transfer rate and not making the low limit hot enough, soon enough. Also, make sure to use the conductive grease on the low limit and put the tank insulation back over it to shield from outside air temps.
    Don't get in a rush servicing these.
    Don't worry about adjusting the low limit either, it's not got an adjusting screw on it :)
  • tim smithtim smith Member Posts: 2,226

    one other thing possibly, we have found that some times the internal pump will go off in thermal overload periodically. This causes the tank to never get up to full temp, in turn the external pump never gets to come on. The rise in water temp + the weak thermal overload shuts down the pump. Good luck, tim.
  • Ken, Tony answered your question

    as for the training on Heatmakers we do it with a factory training person from Laars who now make the Endurance which is a souped up Heatmaker if you will. If enough people are interested we will run a school. One day on Heatmaker, one day on Endurance and the last day hands on.

    I do however strongly suggest that those who attend those classes have gone through my basic five seminars first. With those under your belt the Heatmaker and Endurance traing come much easier.
  • Ken C.Ken C. Member Posts: 267
    Thanks, Tony and Tim

    Tony, what you say makes sense. It seems to me like a design flaw - Trianco should not have put the low limit, which controls the external circulator, on a pipe for domestic hot water. Suppose it is late at night, and there is no demand for domestic hot water ... then how long will it take for the external circulator to come on? Regarding the "adjusting screw," I was going to post back that the limit had no screw. Not too many guys like servicing these units, that's for sure.
  • DavidDavid Member Posts: 250
    Once you have a few calls

    under your belt these things aren't hard to service. My only complaint about them is they are not a very robust design.

  • WeezboWeezbo Member Posts: 6,232
    Well thanks or helping me see the light on

    making assumptions based on strap on aquastats that i am used to using and gas boilers strap on aquastats...i seem to have been have made a giant error describing one. i also use sensors that work along the samelines and set point t stats which of course have no screw on them either.the honewell control we use is most often used to turn off and on a fan on a "Unit Heater" although i have used them to control recirculators. there is a new one out made by taco that is used on recirulators used in domestic constant hot water at the faucets and valves in a home. it looks like a snall "tin can" bought onelast month it sences a fall of pipe temerature and "makes "the circulator.The honewell control has a dial on it and that dial may beturned by a screw in the center of it ,either up or down .it is often also used as a means of controling boilers in lag lead formations. Me Really really sorry if i added to your problem in any way .:(
  • TonyTony Member Posts: 608
    It should

    be where it is because it makes sure you have adequate DHW before space heating, just like any other low limit does. It doesn't take much to maintain the buffer tank's temp when you're heating a coil as directly as they do.

    The Endurance is a real kick-a#* upgrade. It modulates and uses a plate HX for DHW. Only 2 complaints I have are the vent's still a PITA to install and the flow switch for the DHW is next to impossible to change.
  • Paul B.Paul B. Member Posts: 62
    Heatmaker low limit

    The low limit should be installed just as close to the tank outlet as possible, if it is installed up above the elbow(where it's easy to reach) it won't sense properly. It's also important to make sure the insulation is back over it.

    If the low limit isn't kicking over than we need to look at why it isn't getting hot at that location.

    Give me a call in the AM at 603-335-6300x562 and we can go through the trouble shooting, and get the boiler back up and running.

    Paul B.
  • Ken C.Ken C. Member Posts: 267
    Tony, I've got a tip for you

    I know firsthand about the flow switch you mentioned on the Endurance boilers. I had to change a leaking one, and also found it "next to impossible" to change. Very tight clearance, you can barely fit your hand in there, plus you can't help but burn yourself on hot pipes. I used a 6-inch (toy) pipe wrench, and even that I only had a few degrees of swing. Now, the flow switch has washers, but since it was so hard to change and I wanted to make extra-sure my replacement didn't leak, I used pipe dope. It didn't leak, but I got a callback because the tenant had hot water, but no heat. My boss came back with me and determined the flow switch was sticking in the closed (open?) position, so that the switch was always making, thus, no heat. This time, my boss changed the part - in two minutes, with no cursing or sweat. The secret? He used a plumber's basin wrench! I wish I'd have thought of that (it took me about one hour with the pipe wrench).

  • Tony, they are

    supposed to have a new vent kit that is much easier to use. If you get in touch with Mark Hughes at Laars 800-900-9276 Ext 5401 or 603-781-4815 or [email protected] he can fill you in on the new venting.
  • Ken C: you can also

    take the side panel off and it becomes real easy.
  • Paul B.Paul B. Member Posts: 62
    New Vent Kits

    That's correct Tim, The new vent kits are a gasketed design, and go together with out silicone or foil tape.

    They are also compatible with the old kits so that repairs can be made. If you go to our website at and go into the Technical documents, LTD # 8 pertains to the new vent kits.

    As for the flow switches, the Basin Wrench is the tool of choice to remove, and re-install. If you are changing one from a plastic switch to a brass one, the wires come out on the opposite side. Instructions are included in the box. Observe the position of the wires coming out of the valve, and the direction arrow or it will be in upside down, and the paddle will be "made" all the time.

    very Sincerly, and a Happy New Year,

    Paul Bock

    Applications Engineer

    Laars Heating Systems,
    Rochester NH.
  • Paul I was unable to find

    LTD # 8 could you give a title or document # for that vent kit instruction?
  • Paul B.Paul B. Member Posts: 62
    Laars technical discussion

    Hi Tim,

    It's in the "other documents" section of the Thechnical documents area. I'll try and post it here as an attachment, and We'll make sure you have some for the next Endurance class.

    Paul B.
  • Paul B.Paul B. Member Posts: 62
    Technical Discussion

    zhi Tim,

    It's in the "Other documents" area of the web site.

    If you can't get the link to work, I can e-mail it to you directly.

    Paul B.
  • TonyTony Member Posts: 608
    Good idea

    I was about an hour doing the one I had go bad. I had to insist the HO go upstairs after I burned myself the 3rd or 4th time. It must be a change I haven't seen if the sides come off now. This one is a 2001 model. I haven't used one since 2/03 (distributor issues that are unresolved).
  • Thanks Paul, I

    downloaded it.
  • TonyTony Member Posts: 608
    Hey Paul,

    Is the Endurance certifiable for manufactured housing like the Heatmaker was ?
  • Ken C.Ken C. Member Posts: 267

    We considered taking the panel off, but it looked more involved than using the basin wrench.
  • kalkal Member Posts: 15
    as if there is side access on ones you didnt install ;) ...

    give me a beak - baptism by fire - that what i have with these - they are almost always in a closet, the last one I had, I had to use a ratcheting box wrench to get lower outside 5/16 nut off , for the lower front cover and then I also had to crush the sheetrock beside it

    two ridgid basin wrenches - you’d think that a crowfoot flare nut wrench is better, not! to big, in the larger sizes, a pair of basin wrenches are better

    and in case you have to change the circulator, don’t!!!
    remove the housing with the 4 cap screws from the front and either change the cartridge avail from Grundfos part# 526062 for the 26-99 and 506173 for the 15-42 , or just take apart a new one and put it on, the old pump shell still in the unit, or you can take the cartridge from the new one and put it into the old motor housing, don’t worry about the ceramic bearing by the face plate end, those rarely fail as they are not exposed to the debris flow – I asked larrs for negative feedback on that method and got nothing – so it’s my new method of choice, - fyi 526062 for the 26-99 has a list price of 115 – so it’s a third the cost of a new pump

    ps the difference between a larrs 26-99 and a street 26-99 besides the 80 bucks, is the connector and grommet – which you can transfer to the new one, and thin rubber gaskets designed for the stainless-steel flanges – those are harder to come by

  • kalkal Member Posts: 15
    for burns: paper towels and cold milk

  • kalkal Member Posts: 15
    for burns: paper towels and cold milk

  • Paul B.Paul B. Member Posts: 62
    Manufactured housing Certification

    Hi Tony,

    The Endurance has not been certified for Manufactured housing. Our Oil products have been certified, and can be used, but not the Endurance.

    Paul Bock

    Applications Engineer,
    Laars Heating Systems
This discussion has been closed.


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