Baxi Luna 310fi - Increasing Pressure Issue

Bentley27

Baxi Luna 310fi - combination unit for in floor (Radiant) heating and domestic hot water.

Domestic hot water works perfect no issue.

As soon as in floor heating comes on, pump starts to circulate. As soon as burner lights the pressure shoots up past 3 bar, the Pressure Release valve lets go and hot water comes out. All lights turn off on the unit and heating stops.

My immediate thought is Expansion Vessel... drained the unit and checked it. No pressure. Pumped Expansion Vessel back up to 1.5 Bar, refilled unit and tried again. Exact same problem. I am assuming I need to replace the Expansion Tank but want to make sure that is the fix before doing so as it is a pain in the *** job. Can I confirm somehow that the Expansion Tank is shot. Anything else that could be the problem?

Any thoughts or recommendations? Thanks!!

Intplm.

That 1.5 bar? I'm not sure, but is that about 22psi to use yanks?😄 Seems a bit high if it is that pressure before start up.
The water pressure and tank pressure should be the same.

Does your system have a automatic feed valve? The tank and feed valve should be at the same pressures.
(I have feeling you already know that) maybe check the feed too?

Bentley27

Thanks! The pressure of the internal unit is at around 1.2 Bar normally... 17 psi. I thought the expansion tank should be a little higher, but I can let some out. The main concern is that the Expansion Tank doesn't seem to be taking the increased pressure... but just with in floor heating. When the burner lights for heating for domestic water everything is fine.

Bentley27

To answer your other question. I have to manually open a valve to put water into the unit if pressure needs to be increased. My guess is that means no on the automatic feed valve.

EBEBRATT-Ed

If you check the expansion tank pressure on the air side of the bladder you have to do it with the tank removed from the system or isolated from the system with no water pressure on the water side of the bladder.

If you find the air side empty then the tank is bad for sure. Or pump it back up to 1.5 bar and try it but it most likely will not last

Bentley27

Thanks. Ya... I drained the internal unit to check the pressure and it was at zero. Then I pumped it to 1.5 Bar and refilled the unit with water. Issue still occurred. I guess I should do the same and if Expansion Tank is at zero pressure again it is shot?

Intplm.

And yes.......it's probably a bad, or too small expansion tank.

Bentley27

That was my thought also. OK thanks all. Any other comments... keep them coming!!

Intplm.

Yes. Air Pressure on the expansion tank, reading at zero , means it has lost its air charge.

SuperTech

What I usually do to fix this issue without ripping into the combi is I install an external expansion tank pumping away from the circulator like I would on any other boiler. I just leave the shot internal tank as is. This makes it much easier to service in the future.

Bentley27

Ah. OK. Where would I install, on the hot piping leading from the Baxi to the In floor heating manifold?

SuperTech

> @Bentley27 said:
> Ah. OK. Where would I install, on the hot piping leading from the Baxi to the In floor heating manifold?

Yes. Usually I like to install the air eliminator, water feed valve and backflow preventer and expansion tank on the supply pipe coming out of the boiler. Then the circulator pump should be next on the supply, pumping away from the expansion tank.

If you don't want to repipe everything because of the current configuration you can install the expansion tank elsewhere and it will function, but the configuration I described is the best way for system performance and air elimination.

Bentley27

Thanks. The Baxi has the circulation pump built in so there is not one separate. When I installed the Radiant System I did put the air eliminator on the Supply Pipe. Looks like that's the right spot. Thanks again for the help... I assume same size Expansion Tank that is inside the unit (10 Litre).

SuperTech

Check out the Amtrol website, I'm sure they have the capacities listed for each tank. The majority of average residential equipment uses a #30 tank. Don't forget to install a isolation valve for future service. I'm glad I was able to help. Good luck with it! 😉

Bentley27

Thanks you!

superdave

How long has this been installed and has it been working ok up intel now?? I tell my guys is to test the ex thank with water in heating system and see if any water comes out of tank. If so then change out tank as needed. if not I have them shut down the boiler and close all valves at bottom of it and drain down at the drain port of Baxi and leave it in 5 gal. bucket with water and pump it up to about 30PSI and see if any air comes out of 5 gal. bucket also look at PSI gage and see if it shows any PSI in (Bar) and give it a few min. about 15.

Bentley27

Thanks superdave. The unit is at least 10 years old... it has been working fine until about a month ago. I have it just set on domestic hot water now and it is working fine. The only expansion tank is built inside, there isn't an outside one... although I have access to the air valve on top. I will check the pressure in the tank again before installing any new expansion tanks. Last time... it was zero air pressure when the water in the unit was drained. I pumped up to 1.5 bar and it seemed to hold although I only watched it for a few minutes. As soon as I tried the In Floor Radiant heating... the same thing happened. Escalation of pressure as soon as burner turned on, release of pressure valve and shut down of system.

Chippy

I realize this discussion is old but maybe someone will see it. I have a similar problem in that the pressure relief valve discharges water so there is no pressure in the system and it fails to light up. I have replaced the PRV twice over the years but I am beginning to suspect the expansion tank however the instruction manual says it is pre-charged and I cannot find a a air valve to test/recharge it. It is also at the back of the boiler behind everything and would mean dismantling the whole unit. I was wondering if fitting and external expansion vessel is the answer and if so what size would you recommend.

Chippy

I realise this was a while ago but I have the same issue and do not want to dismantle the system. Were you able to solve the issue by using an external pressure tank if so what size and where did you connect it.