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Boiler pump does not start when thermostat is turned up

Hello, when I turn up my thermostat the hot water boiler circulating pump does not start. I can manually turn on the pump when a switch is turned on, but the thermostat will not actuate the pump. I have two zones thereby two thermostats, neither thermostat will actuate the circulating pump. The fuse panel is all turned on so I am at a loss. Could it be a transformer or something?

Please help me with advice on what to check for.

Much appreciated, Kirk Bentley


  • scrook_2
    scrook_2 Member Posts: 610
    might be...

    a bad pump motor, or a bad control relay, or could be something else.
  • Kirk Bentley
    Kirk Bentley Member Posts: 4
    control relay

    Where is the control relay located?
  • rich pickering
    rich pickering Member Posts: 277

    on (or adjacent to) the boiler. follow the power line back from the pump motor. It should end up at either a control relay or the aquastat.
  • You can manually start the pump when

    the switch is turned on - which switch?
  • Kirk Bentley_2
    Kirk Bentley_2 Member Posts: 6

    There is a separate switch that looks like a light switch that I can turn on that makes the circulating pump run continuously. It is mounted on the side of the boiler. Before when this switch was in the off position, if the thermostat called for heat, it would start the pump. Presently the pump will not circulate unless this manual switch is turned on.

    Not sure, but I think it is the relay, that is also mounted on the side of the boiler in a 4" X 4" box.

    Any help would be most appreciated.....thanks
  • Pull the cover of the

    relay and push in on the relay contact bar and see if the circulator comes on, if it does then take a wire jumper and jump the T - T terminals, if the relay pulls in then it is okay and your thermostat or wires to the thermostat are the problem. If it does not then the relay is bad.
  • Kirk Bentley
    Kirk Bentley Member Posts: 4

    Finally an answer I can run with.....thank-you very much! I'll let you know how I make out...thanks again.
  • Kirk, I just re read

    your post. You have two thermostats so it sounds like with one circulator you may have zone valves is that correct? if so then the zone valves may not be closing to make the end switches, The end switches would go directly to the relay so if jumping out the T - T terminals brings in the circulator you may want to check the zone valves (if in fact you have zone valves).
  • Kirk Bentley
    Kirk Bentley Member Posts: 4

    Hi Tim, yes I have two thermostats and two zone valves with one circulating pump.
    I went down to the boiler room to apply your recomendation of bridging the T terminals in the relay box and found the pump already working properly. When I checked it a while later, the pump was not working even though I cranked the thermostat up to call for heat. When I bridged the T terminals, the relay kicked in and started the pump and consequently the boiler.
    There are 3 transformers including the one inside the relay box. I checked the output on the one that goes to the zone valves and it outputs 24V. The transformer to the Hi/Lo temp switches outputs 26V. I did not check the transformer that is built into and part of the circuit board of the relay. The relay seems to work when I bridge the T terminals. I also checked for continuity to the two thermostats, and they check out okay.

    Could it be one of the zone valves? Is there a way to check the zone valves?

    I really appreciate your help, Tim.
  • What kind of

    zone valves do you have? It sounds like the end switches on the zone valves are not always making contact. Next time it is not running make sure the thermostat is turned all the way up and then jump out the end switch contacts on the zone valve. If the system kicks on then the zone valve head is faulty or the valve may not be opening fully it depends on the type of zone valves you have.

    The system works this way the thermostat calls and powers the zone valves, the zone valves open and close a set of internal contacts (end switch), which is turn is wired to the T - T terminals on the relay. That should bring in the relay which brings on the circulator and the gas valve or oil burner depending on application.
  • Frank_62
    Frank_62 Member Posts: 16

    hi kirk i've been following your posts and your additional info these are my thoughts. you say if you jump across the tt terminals in the relay you bring in your pump and burner burner would only not come in if it was off on high limit. I'll assume,and I shouldn't that you have taco zone valves because they are most common. the 24v transformer that is on the zone valves sends one side of the transformer to one side of the thermostat the other side of the termostat goes to the #1 terminal on the zone valve the #2 terminal on the zone valve goes to the other side of the 24v transformer and one side of the tt on the relay the #3terminal goes to the other side of tt one the relay. tt on the wall closes on call for heat sending power to term.#1 on zone valve which closes sending power to the tt in the relay which closes bringing in pump and burner and sends power to #3 on the zone valve to open the head allowing heat to pass. Keeep in mind the opening of the head can take a few minutes. the part that bothers me is the switch you describe on the pump. if there is a switch in the pump its probaly there to kill power to the pump if it had to be changed. the c1 and c2 terminals on the relay should go to the switch and then to the pump. the c1 terminal should have a black wire or colored wire other than white or green going to one terminal on the switch,then another similar colored wire should leave the second terminal on the switch to one side of the pump. the white wire from c2 should go straight thru the switch box to the other side of the pump. the switch should be in the on position,call for heat leaves the relay thru the switch bringing in the pump. if there is no aquastat to the pump which wouldn't allow pump to come in until water reached certain temp and when you jump the tt on the relay you can bring in the pump it can only be one of two things which you can't find until you have a call for heat and pump doesn't. next time the pump doesn't come in on a call for heat and the burner does take the cover off the relay and see if the square block in the relay below the tt terminals is open if it is check to see if you have 120v on terminals c1 and c2 by putting a meter on each terminal simultaneously set meter ac 150-200v if you have power there carefully remove switch cover and put one side of meter on switch terminal coming in from pump the other side to neutral check power coming into the switch then check terminal on switch going out to pump. I'm thinking bad board on relay or bad switch. Both will break down over time because electricity does that after continued use and will some times cause intermittent problems until it finally goes please be carefull you'll be testing with live power sorry to be so long winded but couldn't explain any other way. by the way if it's not a taco zone valve it's honeywell,white rodgers etc there should be a wiring diagram on the head by the way did you happen to add new thermastats before this problem showed up because you need an heat anticipator setting of .09 to operate system and some of these programable and digital thermostats are not compatible with zone valves good luck
  • scrook_2
    scrook_2 Member Posts: 610

    "heat anticipator setting of .09 to operate system and some of these programable and digital thermostats are not compatible with zone valves"

    You mean 0.9?
  • Frank_62
    Frank_62 Member Posts: 16

    I made a typo thanks for picking that up
  • Kirk Bentley_2
    Kirk Bentley_2 Member Posts: 6

    Hi Tim and Frank. Thank-you very much for replying to my questions. I have two zone valves, one is a PENN and the other is a HONEYWELL.
    I have one conventional older thermostat with the mercury ball inside, and the other is a Honeywell programmable thermostat. Both, at the moment, are working fine. They both actuate the zone valves and, for the time being, the relay is kicking in and starting the pump and then the boiler.
    I have a print-out of your suggestions and again I'm very greatful for your replies and help. I'm not sure why everything is working again, but for the time being, I think I'll leave it alone.
    When and if it fails again, I will trouble-shoot with your suggestions. And if I can not figure it out, like the Terminator says....."I'll be back!"

    Once again guys......Thanks!

    Kirk out!
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