Baxi Luna 24 Fi Help

JamesW

I have a 9 year old Baxi Luna 24 Fi Wall Hung Combo Central Heating/Hot Water Unit. I have never had a problem up till a week ago as follows:  With the control set to either Hot Water only or Central Heat/Hot Water after turning on/calling for hot water the usual ignition sequence goes on and completes. Hot water travels to the faucet but after about three to four minutes the heat starts to dissapate and it doesn't turn back to cold but remains luke warm. The unit continues to run but the hot water does not return to getting hot.

I have checked the pressure valve, the DHW heating switches and diaphram and adjusted the heat level by the dial control all to no avail.

Anyone have an idea what this might be or what to try next.

The Central Heating unit works fine and there is no problem in this area. Just can't get the hot to stay hot!

Thanks all,

James

Alan (California Radiant) Forbes

Baxi

Hi James:



Unfortunately, I don't have a solution for you other than calling technical help at:



(800)461-4657



The company name is Marathon and they are the rep. for N. America.

JamesW

Baxi Luna 24 Fi Help

Should anyone be interested, which it looks like not, the TECH from Baxi Marathon proposed it might be the NTC Sensor or Hot Water Temperature Sensor. Will investigate and post again with results.

Matthew Grallert

plate heat exchanger?

This boiler has a brazed plate heat exchanger?  Could this be the problem?

JamesW

Baxi Luna 24 Fi Help

Yes it has that heat exchanger and that will be the next step should it not be the sensor. Thanks for your reply.

James

Nron_13

HX on baxi

You may need to clean the heat exchanger if the unit is over 5 yrs old i would do this before you change the sensors , has there been any change to the flow rate for the hot water ?

Nron

JamesW

Baxi Luna 24 Fi Help

Wow thanks so much for your imput. The flow has not been hampered. I will attempt to clean out the Heat Exchanger and see if that makes a difference as it looks like it may be a day or so until I can track down and receive a sensor. (Anybody know a good supplier of Baxi parts in the US?)

Cheers,

James

Alan (California Radiant) Forbes

Baxi parts

James:



I order Baxi parts from my local wholesaler who orders them from the local rep. who gets them from Marathon. 



Before you do any more, email Jamie Jackson, the technical director at Marathon:



jjackson@wallhungboilers.com



Don't be upset at the perceived lack of interest here on The Wall.  I've noticed from previous Baxi posts that not many tech's. have ever seen them.

JamesW

Baxi Luna 24 Fi Help

Hello All,

Just an update. I have installed a new HW sensor and cleaned out the Heat Exchanger to no avail. Waiting to hear from the rep at Baxi as to what to try next. Stay tuned.

TFL

Baxi 24fi DIY?

James,

I have a few questions.

1.  Have you had the unit serviced proactively in the past 9 years?

 

2.  Have you asked the Baxi rep (that you are waiting to hear from) who is      available in your area for Baxi Certified service tech?

 

3.  If you are going to take a "DIY" approach to servicing this unit, what is your plan for troubleshooting and diagnosing the issue on your own?

 

Without the proper tools and training, you are dependant on others for free advice and "best guesses" on what the issue is during a time of year where most techs have all they can do to handle the calls they are getting paid for let alone taking the time to give free advice and consultations.

  

 Determining the issue will require specific troubleshooting and diagnostic steps, specialized tools, and most importantly, experience to isolate and identify exactly where the issue is.  Once you have a licenced, Baxi Certified tech in front of the unit, if they can't figure it out they will have the resources to get help and get it resolved quickly and cost-effectively.

 

That said, here is what I think your issue is:

 

When you have a low mass, wall hung boiler, regardless of make or model, there are several factors acting on the unit from the outside.  With low-mass combi units like yours, what is essential is the pressure and volume of gas to the unit.  By design your boiler and many others like it have very little water in them.  Your boiler does not heat the domestic water by passing it directly through the combustion chamber or the "primary heat exchanger".  In the case of the 24fi, It is heated with the secondary or "flat plate" heat exchanger.  When you open a hot water tap, this causes a pressure drop on one side of the DHW diaphragm, while on the other side the domestic water pressure is greater and allows the 3 way diverting valve to travel to the DHW production position.  When this occurs, the hydronic water that was being pumped out of the boiler to your heat zones is diverted to the internal flat plate heat exchanger.

 

Once domestic water is flowing through the flat plate and hydronic water has been diverted to the flat plate, thermal energy is transferred from the hydronic water to the potable water.  Therefore, the boiler is maintaining the domestic water temperature set-point by changing or "modulating" the hydronic water temperature to match the rate of transfer.  This rate of transfer is changing several times per second based on rate-of-flow, incoming temperature, changing flow etc.  The boiler maintains or drives the temperature of the hydronic water (which heats the domestic) by constantly changing or "modulating" the gas valve. 

 

When your boiler was commissioned 9 years ago, the incoming gas pressure was measured and adjusted to meet manufacturer requirements.  Once that was established, your boilers gas valve was calibrated or "set up" based on that incoming pressure.  If the incoming pressure changes (this is where your gas regulator / meter comes into play) a significant amount, this can change the energy input to the hydronic water which is heating your domestic water.  Of course you won't necessarily notice this on the heat side of things unless the BTU input were to drop below that required to heat your home at any given time but, you WILL definitely notice it in the shower! 

What I am trying to say is there is no better place to get an idea of what is going on with regard to energy input to your boiler than the shower.  There are no mixing valves, tanks, etc., what you are feeling in the shower is exactly what is going on moment by moment in terms of energy input at the boiler.

 

Your boiler does have a flow limiter that will not allow more than the rated production to pass through it.  I have seen a few situations where these have failed ( potable water pressure exceeded maximum rating of boiler in all cases) allowing way more water through the unit than it could possibly heat based on the rise and GPM.

 

I suspect the "old girl" just needs a good top to bottom physical, gas pressures confirmed and calibrated at the supply and on the units gas valve.  Most of the Baxi Techs that I work with also will change the diaphragms as part of the standard annual service.  You might also consider a treatment of Sentinel X400 and X100.  This will remove any scale / sludge deposits in your heating system and the boiler itself and make heat transfer more efficient.  The X100 is GREAT for your circs too!

 

It could be a part failure but it doesn't sound like it from here.

 

Call your Baxi rep and get some names of Certified Service Techs and get them over there!  Please keep me posted and enjoy a long, hot shower after they leave!



Please let me know how it goes.



-TFL