Baxi 310fi loses pressure

Baxiboy

Have a Baxi 310 that's only used for heating.
Has been in service over 10 years and always held pressure.
2 years ago it started gradually losing pressure to the point it would drop from 1.5 bar down to zero over the course of 2 weeks. I could see no internal leakage anywhere other than some slight water/corrosion staining coming from the auto vent located on the pump housing.No evidence of active water coming from it though.
However after comissioning the boiler this year the pressure drop is happening much quicker.Drops to zero in a matter of 3-5 days.
I did notice the high pressure relief valve was dribbling at times so replaced it. However I am still experiencing the drop in pressure.
After replacing the safety valve I refilled the system and watched thru several cycles observing a constant venting of air from the auto vent so am questioning if I am losing the pressure thru a possibly faulty auto vent.There's no collection of water anywhere under the unit that would indicate the vent is leaking though.
Also on observation 3 days later after replacing the safety valve the system pressure had dropped to .5 bar and after refilling the system at cold temp with system not running the system seems to hold pressure.

The heating system itself (piping) is buried behind the walls so next to impossible to see if there's a leak somewhere in the system loop.

Could soneone explain how to test the auto vent? Or any other possibilities I should be checking?

Alan (California Radiant) Forbes

Could it be that there's air in the system and your air eliminator is venting that air, allowing the pressure to drop?

Baxiboy

I don't think so. Have tried filling the system and bleeding it at the top most point in the system removing all air and it still loses pressure.
I actually just checked again and it looks like the new safety valve also let out about a cup and a half of water.
Does anyone know if the internal expansion tank is tied into the heating circuit? Starting to wonder that if it is maybe I'm dealing with a blown tank?

Alan (California Radiant) Forbes

Yes, the x-tank is on the heating circuit and like you say, it's probably lost its charge. Drop the pressure to zero on the system and check the pressure on the x-tank. It should be the same as your fill pressure.

Tom_133

If you want you can put an external expansion tank on the heat side, makes life easier (when you need to replace) and cheaper than the internal tanks. Be careful of placement of the new tank, no check valves or shut offs between it and the heat exchanger, less likely for it to not work

superdave

On the Back of old Baxi 310 or 1.310 there is an expansion tank I call a flat pancake. What I do to test is shut the valves on boiler and drain boiler at the drain valve by the pump housing and leave it open and air test it to see if air leaking out drain if not leaking big I test up to 30PSI and make sure the bar gauge stay on 0. and complete tune up and at the end I check to see if drop. If it holds I then drop it down to the needed PSI of system. Plus you also need to remember that this boiler holds less than 1 gal. of water so to loss PSI in a system it does not have to be a big leak at all it could just evaporate before you can see it.

Baxiboy

superdave said:

On the Back of old Baxi 310 or 1.310 there is an expansion tank I call a flat pancake. What I do to test is shut the valves on boiler and drain boiler at the drain valve by the pump housing and leave it open and air test it to see if air leaking out drain if not leaking big I test up to 30PSI and make sure the bar gauge stay on 0. and complete tune up and at the end I check to see if drop. If it holds I then drop it down to the needed PSI of system. Plus you also need to remember that this boiler holds less than 1 gal. of water so to loss PSI in a system it does not have to be a big leak at all it could just evaporate before you can see it.

Thanks for the info.
As the boiler is over 10 years old and possibly as much as 15 years I just went ahead and replaced the expansion tank feeling that had to be the problem and probably at the end of it's life expectancy anyway. Sure enough the old tank was completely filled with heavily rusted water with zero air charge in it.
I installed the new tank without checking what the pre-pressurized charge was but did check that it had a charge.
I filled the pressure in the system to 1.2 bar. The system does not have any type of make-up water installed.

Watched the system cycle for close to half an hour and only observed a handful of drips coming out of the pressure relief valve so left it running. Returned yesterday to find roughly a 1/4 cup of water in the bucket I left to collect any blowoff. System pressure was between 1.1 and 1.2 bar.
I will return today to see how it performed and also to check the tank charge to get the set-up set correctly.

I do have a question or two if you don't mind as it seems you are extremely familiar with this boiler and I am very much a layman.
What should the normal ballpark cycle time be? Both running and down time..
I realize a lot of factors enter into that question such as structures ability to hold heat etc.
But if the thermostat is set at 70 and assuming the structure is well insulated, is there a proper cycle time the boiler should have?
I ask because the boiler seems to cycle on every 5-6 minutes or so for 2-3 minutes at a time and the neon temp indicators on the unit just reach the 50 mark when it kicks on and 70 when it kicks off. The temp setting on the boiler is set at about 1/4 to 1/3 of its range.

Thanks for your help!

superdave

Send photos of boiler system and also with the front door down so I can look to see what it is set for. I tell people to think of controls nobs as a clock and tell me what time is it on 12:00 min and 9:00 in max. There are dip switches on main PCB board that will change the stand by time of boiler also do you know if they set the boiler up on high fire 5.62 inches and low fire .72 inches of W. C. on outlet of gas valve. Do you know what your heat is needed in BTUs you can also make this boiler custom to only what you need to so you are not short cycling the boiler.

Baxiboy

Will take pics
Hate to say it, but i installed the boiler. So not professionally installed.
Never set it up for high or low fire as i don't have the gauges for doing that.

It's plumbed very basically.
Cold water supply line with no pressure regulator direct to the unit.
Baseboard heat plumbed directly into and out of the unit.
No separate zones , no valves of any kind in the loop.

I tested and performed you air test on the new expansion unit.
Holds air just fine.
Took the pressure up to 28 psi. Holds air with no leaks so set the pressure at exactly 1 bar per the guage on the foot operated pump I use. Filled system with water to 1 bar as well. The auto vent on the pump is working and bleeding air.

It is still leaking at the drainage port of the brand new Apollo 30lb relief valve and losing enough water ( a little over a cup) to drop pressure to zero in 2 days.

Is the auto vent able to vent the whole heating system?

Pics are attached so you can see where I have the system temp set as well as how the system is plumbed. Also a pic of the new relief valve that I replaced the original Watts M335 with.

Baxiboy

more pics

superdave

If you can take one more photo backed away so I can zoom in I can see what is going on. Also the 30PSI relief should be mounted upright so if any debris will not get on seat of valve. also make sure your PSI is right use anther gauge to make sure the Baxi one is not off or plugged up with debris.

Baxiboy

When you say upright on the relief valve can you please explain?
The exit of the valve is pointed straight down same as the original was.

Will post another pic tomorrow and double check the pressure as you say of the Baxi gauge.

But again, does the auto vent vent the whole system on its own?