Baxi Luna issue

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MikePlummer

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Hey,

Baxi Luna 310 Fi combi boiler


I generally don't get into extensive service on gas appliances.
Had a customer call with "no hot water at shower" but has very hot water at lav and kitchen sink. I suspected moen cartridge so I replaced it.
After nosing into it more, there is hot water when using the shower head, but not when using tub spout, unless moentrol valve is open to allow only a small amount of flow then it gets hot.
this tells me the boiler is not keeping up with the higher flowrate of the tubspout vs showerhead or sink faucets.
This boiler has been in for a few years I believe and this problem only started after the original installer performed a service on it and changed a diverter inside the boiler that controls the flow for heating/domestic water load.
There shouldn't be any control required for heat vs domestic flow as there is no call for heat, just to be sure I turned the boiler to only domestic hot water mode and the problem remains, making me suspect its not the diverter itself.
Any ideas what else could cause this?
 

Dana

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The thing can deliver 100,000BTU/hr, which is enough for a shower flows, but pretty marginal for tub fill rates. It's possible that the heat exchanger is liming/scaling up if this is a hard-water area, but whatever the service guy hacked inside the boiler is the more likely culprit, and you may not be fully backing out whatever tweaks he made. Did changing modes make ANY difference? (Measure the water temps at the faucet in both modes, running at least 10 gallons in each mode.l)
 

MikePlummer

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thanks for the quick reply.

the previous guy simply removed the diverter valve assembly as a whole and replaced it with a new replacement - I wouldn't say he "hacked" anything in.

secondly changing the mode made no difference at all.

I got the service manual online and it doesn't show any procedure to adjust the diverter assembly.
 

Dana

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If it screwed up the DHW output, intentional or not, it was hacked. Was it really the right part? Was it installed correctly? If the change in performance was concurrent with the swap out, it's a flag. Why was it changed out?
 

Jadnashua

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SOme of these things use a flow restrictor to help ensure you can get enough heat rise. If he changed that, allowing more flow, it will never be able to get as big of a delta-T as it did before.
 

MikePlummer

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As far as I can tell without pulling it back out it looks to be the same assembly as he took out, it appears that everything is where it should be as far as connections to it. he is a local heating contractor that I work with often and is professional in workmanship.
I do agree that the new problem coinciding with the part swap is not coincidental, but in fact something during the process caused this.
I was suspecting that the filter in the flow restrictor may need cleaned and that the heat exchanger has likely never been flushed.

thanks for all the help so far guys
 

Jadnashua

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On one (long since replaced) boiler I had, they specified various restrictors depending on how the burner was jetted...the external appearance is pretty much the same...it may have been replaced with a larger one. The only way to tell is to look very carefully, and maybe even check part numbers. Some may be marked on the outside. Try this: at an unrestricted faucet (say the WM supply), run the hot out full force and measure the flow rate into a bucket. Compare that to what the boiler says it should have for a flow restrictor. You may need to do this for a few minutes to equalize things between the tempering valve and what may have been stored inside while the boiler comes up to full temperature (not much, but it could skew the results - you want steady state, and that takes a bit of time to achieve).
 

Scott Straus

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I have a Baxi Luna 310 Fi combo boiler. We lost our heat and water a few weeks ago and a new board was put in. We have heat, now, but getting hot water has been frustrating. We have 4 places for hot water - the shower, the bathroom sink, clothes washer, and the kitchen sink. Most of time, the water is cold to the shower. If it does get warm, it only lasts for a half minute. Then it goes ice cold again. The kitchen sink inconsistently goes hot and cold. At the bathroom sink, it seems to always stimulate the demand for hot water. We have learned to have that water running when attempting to take a shower or use the kitchen sink. I don't think this is normal or intended, and it costs us money to have to keep running hot water, albeit at a low flow, just to get hot water to the shower and/or the kitchen sink. Do you know why this unit is behaving in this manner and what we can do to have it fixed?
 

BadgerBoilerMN

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All tankless water heaters must be serviced by qualified personnel on a regular, semi-annual minimum, basis. We work on Baxi Luna, factory trained on Navien, Takagi, Rheem, Rinnai, Bosch etc. You start with the proper installation and follow with regular service, or get used to cold showers. '

Baxi Luna 310 Fi is a combi-boiler. Generally more complicated than anything your local plumber is qualified to work on and you should not let anyone install any such appliance without proof that they can a will service the unit in future.

We start all of our orphaned combi-boilers with a good cleaning, fire and more particularly water side. Flush, clean and treat the fine movements, diaphragms and "O" rings that make the thing run.

We use the Fernox PowerFlushing machine and even then need to pull and replace parts on neglected units including the Triangle Tube Excellence and Navien combis.
 
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