Explain Cold Start Boiler and Aquastat Settings

abro42

I have Aquastat L7224-1002 and Buderus boiler G-115 w/ no DHW. Taco controller SR-506 and AZEL non-programmable TT set for 68F. Floor temp shows 72 and temp dif at TT set for 2 deg. Call for heat at temp Dif -1 deg and works great at TT. Only 1-ZONE is heated at the moment, other ZONES TT set at 55 degrees. All of this inherited w/ home we purchased last Nov and huge oil bill last winter.

Can someone pls characterize the operation of an Aquastat L7224-1002 controller in relation to boiler temp's and use of a TT for cold start boiler application??

(a) I have HL=160F, HLd=20F, LL=off at Aquastat. The boiler seems to cycle from 140F (ON) to 160F (OFF). No ODR in use. Are these settings correct??

(b) Sometimes TACO SR-506 shows ZONE Red LED ON for ZONE being heated and no call for heat at TT - is this correct? Boiler will start under this condition.

(c) I can post more info relative to temps when boiler comes on and off but need help in understanding proper operation of Aquastat for cold start boiler. Boiler was just cleaned and technician says stop "overthinking". We have heat and love radiant heating but refuse to pay high oil bill....dah!!!!!

Thx guys ...learned so much here at this forum and think I need a better tmp controller at boiler. Can you recommend??

Robert O'Brien

> @abro42 said:
> I have Aquastat L7224-1002 and Buderus boiler G-115 w/ no DHW. Taco controller SR-506 and AZEL non-programmable TT set for 68F. Floor temp shows 72 and temp dif at TT set for 2 deg. Call for heat at temp Dif -1 deg and works great at TT. Only 1-ZONE is heated at the moment, other ZONES TT set at 55 degrees. All of this inherited w/ home we purchased last Nov and huge oil bill last winter.
>
> Can someone pls characterize the operation of an Aquastat L7224-1002 controller in relation to boiler temp's and use of a TT for cold start boiler application??
>
> (a) I have HL=160F, HLd=20F, LL=off at Aquastat. The boiler seems to cycle from 140F (ON) to 160F (OFF). No ODR in use. Are these settings correct??
>
> (b) Sometimes TACO SR-506 shows ZONE Red LED ON for ZONE being heated and no call for heat at TT - is this correct? Boiler will start under this condition.
>
> (c) I can post more info relative to temps when boiler comes on and off but need help in understanding proper operation of Aquastat for cold start boiler. Boiler was just cleaned and technician says stop "overthinking". We have heat and love radiant heating but refuse to pay high oil bill....dah!!!!!
>
> Thx guys ...learned so much here at this forum and think I need a better tmp controller at boiler. Can you recommend??

A is correct. Off at Hl on at HL minus diff.

B. Without knowing how it's wired, c

> @abro42 said:
> I have Aquastat L7224-1002 and Buderus boiler G-115 w/ no DHW. Taco controller SR-506 and AZEL non-programmable TT set for 68F. Floor temp shows 72 and temp dif at TT set for 2 deg. Call for heat at temp Dif -1 deg and works great at TT. Only 1-ZONE is heated at the moment, other ZONES TT set at 55 degrees. All of this inherited w/ home we purchased last Nov and huge oil bill last winter.
>
> Can someone pls characterize the operation of an Aquastat L7224-1002 controller in relation to boiler temp's and use of a TT for cold start boiler application??
>
> (a) I have HL=160F, HLd=20F, LL=off at Aquastat. The boiler seems to cycle from 140F (ON) to 160F (OFF). No ODR in use. Are these settings correct??
>
> (b) Sometimes TACO SR-506 shows ZONE Red LED ON for ZONE being heated and no call for heat at TT - is this correct? Boiler will start under this condition.
>
> (c) I can post more info relative to temps when boiler comes on and off but need help in understanding proper operation of Aquastat for cold start boiler. Boiler was just cleaned and technician says stop "overthinking". We have heat and love radiant heating but refuse to pay high oil bill....dah!!!!!
>
> Thx guys ...learned so much here at this forum and think I need a better tmp controller at boiler. Can you recommend??

You're referring to thermostat as TT when that nomenclature is commonly used for the thermostat terminals on a relay such as a 7224.
A. Yes. Off at HL, on at HL minus differential

B. Typically the end switch (XX) on the zone panel is wired to TT on the 7224,providing a demand as long as any zone is calling.

HVACNUT

First, don't go by $$, go by gallons, as prices fluctuate.

The G115 is how many sections? 3,4,5?
You can download the (free) Slant/Fin heat loss calculation app and see if the boiler is sized correctly for your home.
A nice Thanksgiving weekend mini project.

You've only had one winter in the home so you don't really have anything to compare it to.

The settings on the aquastat seem ok. You could widen the differential a bit. A call for heat without the burner firing should mean it hasn't hit the 20° differential yet. If that's not happening, then something else could be going on.

To me, (and I could be wrong) a 2° diff on the thermostats is too wide with radiant. Radiant zones should be set up for constant (or near) circulation for even temperatures.

Do you know what the supply and return temperatures are on the radiant zones? What model circulators and mixing valves are being used?

Rather than the heating system being the culprit, it could be the tightness, or lack thereof of the homes envelope. That's why the heat loss calculation is important.

John Abbott

What are the floor coverings? type of radiant installation ie: staple up/ plates /embedded in concrete/gypcrete overpour etc.
your aquastat settings are probably ok the important thing is to keep the return temp at 140 or above,to prevent condensing inside the boiler passages.This is the generally accepted return temp for non condensing boilers.This is usually accomplished with primary secondary piping. I have seen the Buderis boilers installed without primary secondary piping and the installer removed the baffles from the boiler to raise the return water temps.This is a REALLY bad Idea as as it raises the combustion gas breeching temp which means you are wasting a LOT of heat up chimney or through the wall vent..What controls do you have beyond the aquastat? ALL radiant systems should have outdoor reset as a previous poster said radiant and especially high mass radiant should have near constant circulation at appropriate temperature base on the outdoor temp.we have very sophisticated control systems available today which when set up properly accomplish this seamlessly. radiant is a very efficient method of heating but only if installed and controlled appropriately.As another member mentioned you may have a poorly insulated building envelope or improper or inadequate floor insulation for the radiant.