New System Short Cycle Help

[Draven8795]

I just hooked up my radiant system. Weil Mclain ECO 70 boiler with a taco 4 Zone relay only one zone hooked up at the moment. It has a tekmar 561 thermostat with a floor sensor hooked up.

It gets to temp, 50. But then the thermostat keeps calling for heat which is short cycling my boiler over and over and over the temp doesn't drop from 50. Reading the directions when in radiant mode the thermostat is PWM. Is this causing the short cycle? Should i turn this off and just let the air temp control it? I don't mind an over shoot for this as it's a garage zone I'd just rather have the boiler run longer.


Has an ODR on with min at 80 and max at 120 with outdoor temps from 0 to 70.

Any insight would be great let me know if you need some more info on the setup.

 

[crashcrater]

You should have a differential adjustment on the boiler controls.You can set it so the boiler temp drops how ever many degrees you want until it starts up again and runs to max set point and shuts off again.They are 2 separate adjustments.One is for max temp i set mine at 200 i think.The other i set for a 30 degree differential cooler for the boiler to start up again.Mine has honeywell controls and they are dials with degree marks-hope this helps

 

[Draven8795]

Ok i think my max setting is set to 200 and can't be changed. I do have a setting right now called modulate on which says "The temp must drop this many degrees below target temperature for the boiler to come on when a call for heat is present on heat input"

Is that what i'm looking for? It's currently set to 5. Increase that?

 

[Draven8795]

What i think my main issue though is that i have the stat set to be at 50 degrees. The Stat is currently reading 50 degrees but is still making a call for heat. Why would it do that if it was working as i think it should and not call for heat unless it drops 1.5 degrees. I think the PWM might be screwing with it, in that case would setting the mod temp to 10 help that and only cycle the pumps and not the boiler?

 

[crashcrater]

Ok i think my max setting is set to 200 and can't be changed. I do have a setting right now called modulate on which says "The temp must drop this many degrees below target temperature for the boiler to come on when a call for heat is present on heat input"

Is that what i'm looking for? It's currently set to 5. Increase that?

Yes i think that is what you are looking for.Yea-increase it.When there is still a call for heat and the boiler has shut off beacause it reached 200 the circulation pump will still run and the boiler wont fire until it has dropped 5 degrees inside the boiler. That setting is too soon. Max setting sounds good my unit has a adjustment for that yours may not. Maybe you should increase the modulate at smaller increments to see what it will actually do. You will probably wind up around 30 degrees difference to be happy with when you are done.Anotherwords look at your boiler temp gauge and have it drop around 30 degrees before it fires again

 

[sstec]

My Tekmar stat with slab sensor looks at both slab temp and room air temp and both must be satisfied. Mine short cycled until the whole building was up to temp. sstec

 

[Draven8795]

My Tekmar stat with slab sensor looks at both slab temp and room air temp and both must be satisfied. Mine short cycled until the whole building was up to temp. sstec

Mine was up to temp i set the floor min to be at 45 and left the air temp at 50 to just see what the stat would do. Stat read 50 and it kept calling for heat and not calling for heat. The floor temp was always above 60.

I decided to turn off the floor sensor and the radiant heat setting and just let it act like a normal air thermostat. Today it ran for only 4 hours and it maintained an air temp of 48 with the stat set at 48 all day and the temp out side is 0F right now.

I might wind up calling tekmar i have no clue what this stat is doing in radiant mode with the floor sensor.

 

[Draven8795]

Yes i think that is what you are looking for.Yea-increase it.When there is still a call for heat and the boiler has shut off beacause it reached 200 the circulation pump will still run and the boiler wont fire until it has dropped 5 degrees inside the boiler. That setting is too soon. Max setting sounds good my unit has a adjustment for that yours may not. Maybe you should increase the modulate at smaller increments to see what it will actually do. You will probably wind up around 30 degrees difference to be happy with when you are done.Anotherwords look at your boiler temp gauge and have it drop around 30 degrees before it fires again

On mine the max supply is set to 120 right now actually as it's 0F here. The highest i can set that mod on diff temp is only 10 degrees and I don't see any settings to change that modulation itself.

 

[Draven8795]

Ok after doing some more research I see what the PWM thermostat is supposed to do. I just felt it was short cycling the system like crazy by turning it on for a minute and then off again. I could here this happening all the time. Do i just put all the settings back so it uses the PWM setting and let it's do it's thing in the hope it learns what it needs to do to maintain temp?

 

[sstec]

This is from page 10 of the installer manual. Do you have it set at 100% and do you have the slab temps set for min and max? sstec

Regular Heating -----------------------------------------------------
W1 relay is on when the air temperature falls 1.5°F (1°C) below the Heat To setting.
When the temperature reaches the Heat To setting, the relay turns off.
Radiant Floor Heating------------------------------------------------
When Radiant Floor Heating is selected in the setup menu, the W1 relay operates
using Pulse Width Modulation. This improves comfort for radiant systems with high
mass floors.
• 100% on time at Heat To setting -1.5°F
• 50% on time at Heat To setting
• 0% on time at Heat To setting + 1.5°F
Floor Sensor for Radiant Floor Heating -------------------------------
If a floor sensor is connected, floor minimum and maximum settings are available.
For a combination of air and floor temperature control, leave the internal air sensor on
in the setup menu. A floor minimum can be used to prevent a fast drop in temperature
caused by receding solar exposure. This operation is recommended for areas heated
by afternoon sun through large windows. When the sun sets, it can take a long time
for the floors to get warm again. This may cause the room to cool off too much in the
early evening. A floor minimum setting can help with this condition by maintaining a
floor minimum temperature. Keep in mind the floor minimum temperature will override
the air temperature, and if set too high, may overheat the room.
A floor maximum is recommended for rooms with hardwood floors. Setting floor minimum
and maximum temperatures is a way of enhancing the comfort of the living space while
protecting floor coverings

 

[Draven8795]

Yea i've read that about 10 times now trying to figure this out, ha. There's no setting other than just stating that it's a radiant floor system with a floor sensor. I had the min set at one point but not the max. I'm not exactly sure what to set the min for now. I want to leave the temp in the garage at 50 always.

I guess to make this the most simple as i may have provided to much is that at night I can hear the boiler turning on and off and only running for a minute even the the heat is set to 50 and the temp reading on the thermostat is also 50. So it's short cycling for seemingly no reason that I can understand.

 

[yeldogt]

You want to try and match the water temp to the need .... what return temp can the boiler take?

My radiant systems never use 200 degree water. They go to 180 when loading the indirect water tank ..otherwise they are heating the floor with a 25 degree delta.

Most floor temp sensors are used to protect from solar gain .. or used when only warming and in combination with a secondary ducted system. They make lousy room thermostats.

My guess is the high boiler temp is causing the short cycles -- in combination with oversizing. what the heat load and boiler output. you may need different piping.

 

[Draven8795]

the garage is 1200 sq ft with 1500 ft of tubing and 5 loops. I'll have on more zone in the future with two loops and 600 sqft but i'm still working on that addition.

I actually took your suggestion into account and went and lowered the max supply temp to 117 last night from 120 so the ODR is the only thing controlling the temp now. So much for this fancy thermostat. So it's just been burning all night. I'm going to go lower it a little more today and see what that does to get it to hold at a steady 50.