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Help with Baxi thermostat and "Attenuated Outside Temp"


First time posting.

Last year, I bought a new boiler and had the thermostat changed to a Baxi QZZ73. A while back the manual for the t-stat disappeared and I know that some buttons got inadvertently pressed. I finally got a hold of THE manual and it has "heating engineer" controls that I never even knew existed. Way too much info. Worse, I think some of those controls have been messed up.

On in particular has to do with "Attenuated Outside Temp" (line 53, heating engineer section).

This morning at 8, the thermostat kicked in as usual. At 9 when I came downstairs, the actual room temperature was at 59F. It wasn't until 1PM that the room temp finally made it to 65F.

A few days ago, I had also noticed that the outside temp was flashing - it never used to flash - and this morning, in a moment most unwise, decided to access the heating engineer section.

The "Attenuated" outside temp mistakenly got reset by a person who shall remain namelss. According to the manual, when this is done: "the attenuated outside temperature is reset to the actual outside temperature." The reading for line 53 is now 30F. I know it was lower before the accidental reset. I checked online for the outside temperature. It's 20.2F. So I'm confused. Also, the outside temp that can be checked by pressing the "info" button flashes at 26F. Like I said, I had noticed it flashing a few weeks ago, so I'm suspecting that a combination of buttons may have inadvertently got pressed a while back...

1. Is it normal for a house to take 5 hours to go from 58 to 65?

2. If it's not, is it possible that a button or combination of buttons got pressed on the t-stat making some function not work optimally? Would this "Attenuated" vs "Actual" have something to do with it?

3. Is it time to call a "heating engineer" and can I just look up "heating" and call someone with experience with a Baxi?

4. I'm not that dumb (usually), and pretty handy. Is there anything I can do?

Thanks for any help,



  • Empire_2
    Empire_2 Member Posts: 2,343
    Good morning...

    Unfortunately, I will take a while to read the manual, but I have some Q:'s:  Describe your boiler, house size, climate in winter where you live, Where is the original contractor?  If I received a call from you as a customer, I would have to not only read this manual like you did, Find out what the original contractor was trying to achieve, assuming the outdoor reset is enabled, are all the controls and sensors installed and are the hooked up correctly.  Just to name a few.  That's why I asked where the contractor is to back up his work.

    My  .02

    Mike T.
  • lokilo
    lokilo Member Posts: 3
    Thanks for response... still somewhat a mystery...


    Thank you so much for your reply. Funny too, because I saw it right as a heating contractor was here checking over the system. He wanted to know what you had to say... !

    To answer your questions:

    I have a Baxi Luna 380 condensing gas boiler.

    1200sq ft old house (two floors). The walls got insulated last year. Still a wee-bit drafty (old single pane windows, with storms).

    I live in Maine. Cold winter this year, though unfortunately all the snow is south of us... :(

    After I started this thread last week, there was one other control I messed with: the heating curve slope (line 70). I hiked it up to 40 b/c I read that by increasing this, "the flow temp will be raised when the outside temp drops." Since doing that, I noticed that the house was heating up more quickly and nicely. I was almost ready to cancel my appointment this morning but thought better of it. Maybe I shouldn't have messed with that parameter?

    Today, the heating contractor came and called Baxi. They went through all the controls and made sure everything was set right, which included making sure that heating curve slope was set back down to 24. Good thing I didn't cancel. Also found out that resetting the Attenuated outside temp" was not a bad thing.

    He checked the boiler, all the controls on the thermostat... everything looks good.

    Two possible issues:

    1. At one point he suggested that if I hear "babbling brook" sounds coming from the pipes when the boiler kicks in, the pipes could need to be purged. I do hear those sounds. So in trying to demonstrate to him, I turned up the thermostat hoping the boiler would fire up. It did, but no babbling brook sounds. Figures.

    2. The outside sensor is placed on the SW side of the house, close to the flue exhaust, and it is now in direct sunlight. It gets direct sunlight from about 11AM to 3PM. On the t-stat, the outside temperature reads 34F. It's currently 24.4F here. Heating tech is thinking the outside sensor needs to be moved and placed in the shade. Maybe this is why the boiler is not firing up/modulating correctly? It thinks it's warmer outside than it really is. (That said, at 8AM last week, it would have been in the shade...). It's been over  1 1/2 hour since I've raised the t-stat from 65 to 69 and the room actual temp is 67. (Last Friday, when I really noticed the issue for the first time, it took 5 hours to go from 59 to 65, with outside temp of 20.2F)

    As I told the heating tech, I didn't notice this issue last year b/c when I worked from home, I was usually in my office upstairs, which is always warmer. Now that my roommate is gone, I usually spread my work out on the dining room table downstairs. So this is the first winter season that I get to see how quickly the house heats up downstairs.

    I've scheduled a regular one-year servicing with the heating tech guy. He'll be back in about 1 week. Between now and then, I'll note how long the house takes to heat up, conditions, temp, sunny or not, etc.

    Thanks again for any input. He's sort of scratching his head as well...

  • lokilo
    lokilo Member Posts: 3

    2 1/2 hours since I raised the t-stat from 65 to 69, and the room temp is 68.

    Also, I should have clarified that when the heat tech was going everything over with Baxi, I believe that the only adjustment had to do with the heating curve slope. Everything else seemed fine.
  • Empire_2
    Empire_2 Member Posts: 2,343
    edited February 2010
    Awsome Support by the tec...:-) Now,:

    Quickly,... yes the outdoor sensor should be moved to an area of the house where it is not affected by Sun, snow, or any other outside source that would throw it off.  Since I think it's great that the Tec came back shows a lot of class.  Your heating curve:  This is an area of design preference that I could change at will to meet the demand and of the structure at ANY given outside temp.  Each state has what is called Degree Day's, usually can be obtained from Internet, (search Degree Days Main, Sept -March.  This is an important number in that it canl be plugged into "Right J" heat loss calculations and we can determine where on that curve I want that boiler to operate temp wise.

         I know it's easier said than done and I do not expect to govern your system, But I am darn curious of how much base on the first floor, what size, and supply water temp at "Let's say.............20* - 35*. ?  At 20* I could Max out your boiler at 190* or 160* Depending on the Ratio set on your Curve.  Everything is dependant on another and so on and so on....


    Mike T.

    P.S.  I'm a Sloooooooooooow Typer:-) 
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