Boiler/Baseboard System - Pump not always running

lilweezy29

Hello all,

I have a Gas Boiler that is running a baseboard heating system. The Boiler runs and switches off at the desire temp (165 at the moment, will explain more).

The pump on the other hand does not get triggered until 3-5 minutes after the boiler has reached its max temp. This results in the hot water sitting in the boiler and not circulate, causing temps to rise 20 degrees higher than what the aquastat is set to.

Finally when the pump kicks on, the water circulates through the system fine and we get a few minutes off heat until everything cools down because a small percentage of the water in the system was being heated. Then the boiler kicks on shortly after to try and keep up.

It seems to me the system is running in an extremely inefficient manner. Any advice would be appreciated!

Boiler - Weil Mclain CG-5-SPDN
Pump - Grundfos UPS15-58FC
System - Baseboard with a 5 loop manifold

yesimon

Probably because it's trying to prevent flue gas condensation which will corrode your boiler prematurely. You probably shouldn't be changing this behavior.

EdTheHeaterMan

Weil Mclain CG-5-SPDN is a very old boiler or a more recent boiler. What is the Series of the boiler and the CP number of ot is still there?

If it is one of the early boilers then the circulator pump is not original to the boiler.

lilweezy29

EdTheHeaterMan said:

Weil Mclain CG-5-SPDN is a very old boiler or a more recent boiler. What is the Series of the boiler and the CP number of ot is still there?

If it is one of the early boilers then the circulator pump is not original to the boiler.

Hey Ed, it is a CG series. CP is 3099254. I believe its a fairly old boiler yes but the pump was replaced 2 years ago.

Jamie Hall

And what device is controlling the pump? Aquastat? Mounted where?

lilweezy29

Jamie Hall said:

And what device is controlling the pump? Aquastat? Mounted where?

The pump is controled by the control board in the boiler. It appears the boiler triggers the 120v wire to activate it.

hot_rod

It sounds like the control is attempting to keep the boiler from running in a cold condensing condition. Basically pulsing heat into the system. With low mass fin tube it should not take long to get to steady operation.
How many feet of baseboard are connected? Occasionally systems have more fin tube than the boiler can keep up with.
The fin tube drives the operating condition of the boiler.

Is this a new discovery, or has it always operated like this.
Was the pump size changed in the replacement?

lilweezy29

hot_rod said:

It sounds like the control is attempting to keep the boiler from running in a cold condensing condition. Basically pulsing heat into the system. With low mass fin tube it should not take long to get to steady operation.
How many feet of baseboard are connected? Occasionally systems have more fin tube than the boiler can keep up with.
The fin tube drives the operating condition of the boiler.

Is this a new discovery, or has it always operated like this.
Was the pump size changed in the replacement?

There is about 80ft of fintube spread between 5 loops. The system used have 1 main loop and each baseboard would jump off and reconnect further down the line. Possibly an old radiator system at one point. I cut the amount of fintube and pipe in total in half when we revamped the system. That is when this weird behavior started (At least weird to me). The boiler is rated for 140,000 BTU/hr (Not familiar with how this rating works but seems like more than enough after researching).

I am unsure if the pump size was changed as it was changed before we moved in.

Thank you very much for your help

hot_rod

The boiler manual should show and describe how the pump is controlled. It could be temperature controlled, other controls turn on the pump when the call for heat comes on.

EBEBRATT-Ed

With only 80feet of fin tube the boiler is way oversized. A 50,000 btu boiler would do that job. That boiler should have no problem keeping up with the baseboard

Sounds like you have some type of control problem or control setting. Is there a wiring diagram on the boiler? You need to find out what starts and stops the pump.

lilweezy29

Snippet from the Manual-> https://imgur.com/Rp5t61E




I am unsure but it looks like the circ pump is triggered by the "plug in DPST relay"? Only thing i can't find is a definite explanation of when and how long the pump should run.

Looking at newer Weil Mclain units, it looks like the pump should un anytime there is a call for heat.

Would it be worth bypassing the boiler and powering the pump to see how the system works? The way it is running right now is causing the water to return as low as 110f which may be causing the condensation shut off?

Thank you!

HVACNUT

The circulator should run anytime there's a heat demand, regardless of boiler temperature. Unless someone wired in a time delay relay, the circulator and burner circuit get energized at the same time. The burner will cycle through limit and the thermostat. The circulator will cycle through the thermostat. 

You've got to see if there's 120 volts at the circulator. 
If yes, bad circulator. 
If no, bad relay.
The relay itself pulls right out like a plug and is easy enough to replace. 

lilweezy29

Thanks HVACNUT, i am going to put a meter on it when i get home.

Rich_49

lilweezy29 said:

hot_rod said:

It sounds like the control is attempting to keep the boiler from running in a cold condensing condition. Basically pulsing heat into the system. With low mass fin tube it should not take long to get to steady operation.
How many feet of baseboard are connected? Occasionally systems have more fin tube than the boiler can keep up with.
The fin tube drives the operating condition of the boiler.

Is this a new discovery, or has it always operated like this.
Was the pump size changed in the replacement?

There is about 80ft of fintube spread between 5 loops. The system used have 1 main loop and each baseboard would jump off and reconnect further down the line. Possibly an old radiator system at one point. I cut the amount of fintube and pipe in total in half when we revamped the system. That is when this weird behavior started (At least weird to me). The boiler is rated for 140,000 BTU/hr (Not familiar with how this rating works but seems like more than enough after researching).

I am unsure if the pump size was changed as it was changed before we moved in.

Thank you very much for your help

Please explain how you went about cutting the amount of baseboard and piping in half . BE SPECIFIC , what was removed and how was it reattached ?

lilweezy29

Hopefully this crude diagram helps. In addition to breaking down into loops i also removed unused fintube (like behind the fridge and random parts of the basement). I also cut down on the length of piping in the system by eliminating the "main loop" design that was here.

After identifying what baseboard i needed, i connected each area to a loop on the manifold (one side of baseboard from the feed and the other side of the baseboard to the return).

The system had many issues before but the pump running sporadically was never one of them

109A_5

Hello @lilweezy29,
As previously mentioned as long as the thermostat is calling for heat the circulator should be running. Observing the system and/or testing with a multi-meter may help discover why it is intermittent.

1. Thermostat closes (call for heat).
2. Relay coil 'CR' is energized.
3. Relay contacts CR1 and CR2 close, simultaneously energizing two isolated circuits.
  3a. CR1 supplies power (passing through the limits and safety controls) to the Damper.
  3b. CR2 supplies power to the Circulator (energized it continuously).
4. Circulator is running (continuously) and the Damper opens.
5. When the Dampers opens all the way and the Damper End Switch closes and the Gas Valve is energized.

lilweezy29

109A_5 said:

Hello @lilweezy29,
As previously mentioned as long as the thermostat is calling for heat the circulator should be running. Observing the system and/or testing with a multi-meter may help discover why it is intermittent.

1. Thermostat closes (call for heat).
2. Relay coil 'CR' is energized.
3. Relay contacts CR1 and CR2 close, simultaneously energizing two isolated circuits.
  3a. CR1 supplies power (passing through the limits and safety controls) to the Damper.
  3b. CR2 supplies power to the Circulator (energized it continuously).
4. Circulator is running (continuously) and the Damper opens.
5. When the Dampers opens all the way and the Damper End Switch closes and the Gas Valve is energized.

Thanks for breaking it down for me. I am going to put a meter on the pump and see if it goes from 120v to 0v whenever it shuts off. That should tell me if it's the pump or relay causing problems.

HVACNUT

lilweezy29 said:

Thanks HVACNUT, i am going to put a meter on it when i get home.

It could also be just a loose connection on the relay contacts inside the junction box.
Turn off the power and check all the connections and grounds.

lilweezy29

Update: The pump showed 120v while running and zero anytime it shut off. I also noticed the Boiler flame shutting down before it hit the temp set on the aquastat, didn't notice that happening before.

I found that the Thermostat was not closing the relay even though i had it set to +5 the room temp. After setting the Thermostat up to 80 the system went through 3 cycles perfectly.. The pump stayed running the whole time until i turned the Thermostat back to +3. Then i saw the inconsistency again. I changed out the thermostat and its been working fine for about an hour.

109A_5

Hello @lilweezy29,
With careful observation and a Multi-Meter the defect can be isolated. The relay should be active whenever the thermostat is calling for heat. If the socket for the relay is soldered to a circuit board the solder joints could be failing.
When the thermostat is NOT calling for heat there should be 24 VAC across R and G and the relay should be inactive. When the thermostat is calling for heat there should be 0 VAC across R and G and the relay should be active.

SuperTech

lilweezy29 said:

Update: The pump showed 120v while running and zero anytime it shut off. I also noticed the Boiler flame shutting down before it hit the temp set on the aquastat, didn't notice that happening before. I found that the Thermostat was not closing the relay even though i had it set to +5 the room temp. After setting the Thermostat up to 80 the system went through 3 cycles perfectly.. The pump stayed running the whole time until i turned the Thermostat back to +3. Then i saw the inconsistency again. I changed out the thermostat and its been working fine for about an hour.

Was the thermostat a Nest?

pedmec

Bypass the thermostat so you can eliminate the thermostat as causing the problem, which i don't see. It looks to me like you are not moving enough water thru your loop so you're tripping your hi limit and then you have to wait for the water to cool down below the differential. You had a mono-flo system and removed it and created a direct return. Did you add purge stations at each individual loop returning to your manifold. What type of piping did you use between your baseboard and your new manifolds? is it a radiant manifold or you built it?

lilweezy29

The old thermostat was an old Honeywell round dial. I feel like it is messed up because you have to turn it up pretty far past the room temp before it will close the contact. I bypassed the thermostat entirely and the system ran fine for an afternoon. The Boiler cycled properly (Ran until 165 and turned back on at 145). I have a new simple tstat connected now until i choose a smart one

I hooked the 5 loops up to a radiant manifold. Each manifold has an air separator and each loop has a purge valve at the baseboards. The system is running pretty quiet and i'm fairly certain i've gotten most the air out. From the manifold to the baseboards i used pex piping.

I have almost exactly a 20 degree drop on the return side of the manifold now that it's running smooth.

I will put a meter on R and G when i get home later this week. Thank you for the replies!

hot_rod

The mercury switch thermostats need to be perfectly level to be accurate. The sub base has a place to set a level on it