Circulator pump turning off when burner turns off

Dave_help

I have a Slant Fin boiler, Tekmar 356 control floor heat and domestic hot water. The circulator pump turns off when the burner turns off. The controller shows it is mixing, the relay shows there is a demand but the circulator pump does not run. I’ve changed the aquastat, the 356 control and replaced the relay. It is still not working to heat our floors but our domestic hot water works. What else could it be?

hot_rod

do you have a volt meter to do some checks? Id look at the pump output on the 356 first. Does power drop off to the 356?
Is this a new problem? Or has it always operated this way?

Dave_help

I have 24 volts at terminals 5 & 6 when thermostat is turned down. When thermostat is turned up, burner and pump turning on, 5 & 6 drop to 0 volts. When burner turns off 5 & 6 jump back up to 24 volts. Same measurements at aquastat 0 volts at terminals T and TV when burner is on, 24 volts when burner and circ pump turn off.

EBEBRATT-Ed

The manual is attached. You have to identify the sensors you have (some are optional) to figure out how the control operates. There instructions and troubleshooting in the manual are pretty good.

Follow that and come back with more information. It also tells you how to check the sensors.

356_d_06.pdf

109A_5

How many circulators do you have ?

System pictures would help.

I would think you may need two, one for the DHW and one for the floor (depends on the system). If the aquastat controls the circulator for DHW, how can the Tekmar 356 control it ? The Tekmar 356 has its own circulator control.

" I’ve changed the aquastat, the 356 control and replaced the relay. "

Sounds like a wiring / system configuration issue not a failure of a particular device.

Did the system ever work correctly ?

HVACNUT

Is the circulator wired to the 356, or the boiler aquastat, or something else?

What model boiler?

Dave_help

It has worked for 21 years. The model is a Slant Fin VHS90 direct vent. Here’s some layout pictures. All voltage checked out as it should but when the burner turns off it won’t keep the contacts in on the aquastat which turns off the boiler pump.

when there is no call for heat, terminals 5 & 6 have 25.1 volts. Terminal 7(T) to 9(C-) 26.3 volts until the burner ignites at boiler minimum. 5 & 6, 7 & 9 all go to zero volts and boiler pump turns on and burner turns on. Burner ran to 146 degrees, turned off which turns off boiler pump. The 356 still shows demand and mix out, but the boiler pump is not running. Terminals 5 & 6 are at 25.1 volts, terminal 7(T) & 9(C-) are at 26.3 volts. Thermostat is turned clear up and this all happens within 5 minutes.

Dave_help

Dave_help

hot_rod

5&6 is the power for the tekmar, 24v should always be present unless you turn the power off

If 24 drops off maybe the transformer is overloaded, or fighting another transformer

when 24v drops ftom the tekmar is there still 120v at the transformer? If not something is dropping off the 120v

EBEBRATT-Ed

You have 4 pumps

Mixing

Boiler

DHW

Floor

Is the boiler pump the one shutting off?

I don't see the boiler pump on the wiring diagram.

109A_5

As drawn you have 4 circulators, assuming the DHW one is not a problem. For the floor to get heat the 3 need to run. Are all 3 not running or other. If other which run and which do not ?

Dave_help

Thanks for all your responses! 8 & 9 are power in from transformer. 5 & 7 go to the aquastat burner control on the bottom of the wiring diagram then on to taco007 boiler pump just left of the control on the diagram. Yes, all pumps are running except taco007 which circulates water through the boiler so when it’s off my mix is not getting heated water.

109A_5

Was any work done to the system when this issue started ?

I presently see no control provision for the Boiler's circulator on your wiring diagram, I will check the boiler's manual if I can find one.

109A_5

I see no provision for the boiler's circulator to run without the boiler's burner running. The Orange annotation is the DHW control of the boiler's burner, the Red annotation is the Tekmar 356 burner control. I would expect when the Tekmar 356 contact closure 5 & 6 opens the boiler and its circulator would shut down.

109A_5

Do you have the Hydrolevel Hydrostat 3200 ?

109A_5

If your system uses the Hydrolevel Hydrostat 3200, I would think your system would control it with separate inputs to the Hydrolevel Hydrostat 3200. Gives the DHW priority. It would not solve the present issue of having the boiler's circulator running with the burner off.

If you have a Hydrolevel Hydrostat 3200, did it use 'Outdoor Reset' feature ? Maybe the 'Outdoor Reset' sensor has failed. Which may explain the situation.

One input for DHW and the other for the floor zone heating. An example;

109A_5

Was the resistance of the Tekmar 356 sensors tested ?

109A_5

" when there is no call for heat, terminals 5 & 6 have 25.1 volts. Terminal 7(T) to 9(C-) 26.3 volts until the burner ignites at boiler minimum. 5 & 6, 7 & 9 all go to zero volts and boiler pump turns on and burner turns on. Burner ran to 146 degrees, turned off which turns off boiler pump. The 356 still shows demand and mix out, but the boiler pump is not running. Terminals 5 & 6 are at 25.1 volts, terminal 7(T) & 9(C-) are at 26.3 volts. Thermostat is turned clear up and this all happens within 5 minutes. "

EDIT: Actually this makes no sense;

" Terminals 5 & 6 are at 25.1 volts, terminal 7(T) & 9(C-) are at 26.3 volts. "

If this is true you have lost your call for heat, since the Erie SR100AT relay contacts 5 & 6NO are now open. Terminals 7(T) & 9(C-) are controlled by the Erie SR100AT relay contacts 5 & 6NO.

I suspect the Tekmar 356 terminals 5 & 6 are at 25.1 volts, terminal 7(T) & 9(C-) are at 0.0 volts. Still a call for heat from a zone call energizing the Erie SR100AT relay closing contacts 5 & 6NO but the Tekmar 356 shuts the boiler down by opening its contacts 5 & 6.

Basically using your data above; I suspect the Boiler reaching 146 degrees and that satisfies the Tekmar 356, so it opens 5 & 6. Which shuts down the boiler and the boiler's circulator. However a zone thermostat is still calling for heat. It won't get the heat since the boiler's circulator is now off.

If the Hydrolevel Hydrostat 3200 settings or the 'Outdoor Reset' curve functionality is configured to limit the boiler to say 140 degrees then the Tekmar 356 would not open 5 & 6 terminating the call for heat to the boiler. Since the Tekmar 356 will never see 146 degrees.

If the boiler reaches 140 degrees and the Hydrolevel Hydrostat 3200 shuts off the burner it may keep the circulator running since the the Tekmar 356 would still keep 5 & 6 closed calling for heat.

I'd check the Hydrolevel Hydrostat 3200 settings and if it is set up for 'Outdoor Reset' operation. If the Outdoor Reset is in use but not functioning check the Outdoor Reset sensor for the proper connections and resistance. Sadly I could not find much information on testing the Hydrolevel Hydrostat 3200 Outdoor Reset functionality. Apparently when the sensor it connected and the ratio is set it just magically works with no way to verify it.

If any of the sensors (Hydrolevel Hydrostat 3200 and / or Tekmar 356) are not reading correctly it is hard to expect the system to operate correctly.

Another thing I noticed is according to your piping diagram the DHW does not need the boiler pump for DHW, it has its own pump, but it appears the space heat and the DHW both use the T & TV terminals to fire the boiler. So the boiler pump may be unnecessarily running when actually not needed.

Dave_help

I really appreciate your knowledge and help! There was no work done on the boiler. I just noticed the mix was running a lot. The only thing turning the circulator and burner on is the Honeywell aquastat relay type L8148E. Yes, when it opens 5 & 6 it shuts burner and pump down. I don’t have hydrostat 32 I have aquastat relay L8148E. I do have an outdoor sensor. I checked the resistance and it’s good. I put new sensors on the boiler and mix. Both the 5 & 6 from Tekmar 356 and 24 volt wires from DHW go to terminals T & TV of the aquastat. I changed the Erie relay out for a Taco SR 501-5. DHW comes out of the boiler loop before the Taco 007 pump. Mixing loop comes out after the Taco 007. But if Taco 007 is not running very little water circulates. It seems like the only way it can work is 5 & 6 turn on T & TV (burner and pump through aquastat) burner runs until high limit on aquastat 190° which turns off burner from inside the aquastat. Pump continues to run while there is demand. Then the aquastat will turn burner back on when boiler temp lowers. The 146° off is not normal. See attached pictures and thanks again for your help and knowledge. It is greatly appreciated and I think will help me get to the bottom of this.

Dave_help

Dave_help

Aquastat

109A_5

I'll re-read your post today, but if you are using a L8148 and either the DHW or a floor zone call for heat is by the L8148 T & TV terminals, the boiler's burner and the circulator are commanded on & off at the same time, simultaneously.

Only the L8148's high limit would shut the burner off with the circulator still running. If however the Tekmar 356 is cutting off the boiler at 146 degrees, the boiler will never get to the L8148's high limit if set above 146 degrees.

If you think the Tekmar 356 is the issue opening 5 & 6 I would review the Tekmar 356 settings.

109A_5

Looks like the Tekmar 356 settings are certainly able to go above 146 degrees. Are the sensors in the correct place ?

109A_5

I'd verify the Tekmar 356 is opening terminals 5 & 6 in the 146 degree area and terminal 7(T) & 9(C-) are at 0.0 volts (system demand is still present).

109A_5

With troubleshooting I prefer the surgical analytical approach, however that often requires some knowledge of how the system basically works. I have seen when folks change a lot of things, one piece at a time or all at once, either way that may introduce other issues, and may not repair the original issue. Equipment costs money, so does a pro's time. I consider my time free to me.

You have changed a bunch of stuff, hopefully there are no new issues, the up side is you will have a stock of spare parts.

Is the 146 degree boiler shutdown consistent with a space heating call for heat ? If it is consistent the cause of that behavior needs to be discovered. There are different ways to do this, typically with a voltmeter or the strategic placement of a jumper wire or both methods can be used to isolate the issue.

Since the Tekmar 356 is kind of in the middle of the process that is a good place to start.

I'd verify the Tekmar 356 is opening terminals 5 & 6 in the 146 degree area and terminal 7(T) & 9(C-) are at 0.0 volts (system demand is still present).

Dave_help

The sensors are in the correct place. When I turn up thermostat 7 and 9 go to 0 Volt. 5 and 6 do not unless boiler is at minimum and fires burner. 7 and 9 are still at 0 volt as well as 5 and 6 until burner shuts off. When burner turns off 7 and 9 are still at 0 Volt but 5 and 6 go to 25 Volts. 356 is still calling for heat. Mixing pump and floor pump are running, but don’t get hot water because 5 and 6 are not at 0 volt to run boiler pump. If I remove 5 and 6 from 356 and jump them together boiler pump and burner run. Do you have any other suggestions?

I am in Western Montana, any advice as to how to go about finding a good controls person.

109A_5

This

" When burner turns off 7 and 9 are still at 0 Volt but 5 and 6 go to 25 Volts. 356 is still calling for heat. "

proves to me the zone(s) still have demand BUT the Tekmar 356 is no longer calling for heat. I suspect this is probably because the boiler temperature at the supply sensor has satisfied a setting parameter in the Tekmar 356, so the Tekmar 356 discontinues its call for heat. With the call for heat discontinued the boiler water is stagnant (boiler's circulator is off) and may take a while for its temperature at that sensor location to lower to the point where the Tekmar 356 decides to call for heat again.

It appears to me in your opinion something changed to get to this present behavior. I am having a hard time with the system logic. There seems to be a control path missing which would keep the boiler's circulator active as long as there was demand from a zone. Which is kind of where you started.

Seems to me the relay (presently the Taco SR 501-5, formally the Erie SR100AT) should control the Floor circulator and the Boiler's circulator. (DHW is a different circulator) The wires going to C1 & C2 in the Honeywell aquastat relay type L8148E should be removed from the Honeywell aquastat relay type L8148E and connected in parallel with the Floor pump. So as long as there is zone demand the Taco SR 501-5 relay energizes both the Floor and the Boiler circulator.

This seems to me as a design error and not a recent change or defect.

Just to be clear when the burner turns off and the Tekmar 356 terminals 5 and 6 go to 25 Volts the Burner icon is gone and the Mixing demand is still present ?

109A_5

As I wrote before;

" Another thing I noticed is according to your piping diagram the DHW does not need the boiler pump for DHW, it has its own pump, but it appears the space heat and the DHW both use the T & TV terminals to fire the boiler. So the boiler pump may be unnecessarily running when actually not needed. "

Moving the Boiler's circulator's control to the same control as the Floor circulator's control would also eliminate this situation.