Pentair Mastertemp 400 manifold

LSUser

Member
Dec 30, 2019
6
South Louisiana
Does anybody have a manifold that leaks after it heats up? I replaced one which was grossly deformed from heat exposure. Ran it for a few days thereafter without heating the water--no leaks. Started the heater and . . . leak.
The heater is located indoors.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
12,803
Northern NJ
Can you pinpoint where it is leaking from? Manifold bolts or gasket? You sure the heat exchanger is not breached?

 
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LSUser

Member
Dec 30, 2019
6
South Louisiana
Yes sir. It is leaking from in between the manifold housing case and the manifold bottom plate, on the left and right sides. It does not appear to be leaking from between the manifold bolts and their bores. I will see if the heat exchanger is not breached after i remove the manifold and let you know, sir.
 

LSUser

Member
Dec 30, 2019
6
South Louisiana
This is what the heater did to the manifold. No leaks while pumping the water through the heater for 2-3 days (with the heater OFF). Once the heater was turned on, it didn't take long for the leak to develop. The inside of the heat exchanger tub was dry.

IMG_0234.jpgIMG_0235.jpgIMG_0231.jpgIMG_0231.jpg
Has anyone else seen this happen to their heater manifold?
 

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JamesW

TFP Expert
Mar 2, 2011
17,327
You have a serious problem with the heater.

Is the fan coming on?

I suspect that the heater is firing with no air flow.

Maybe the fan is off or the blower is clogged with debris?

Can you describe the exhaust venting?

Is there an extra exhaust fan?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,214
Tucson, AZ
Can you carefully inspect the metal tub (combustion chamber) of the heat exchanger around the area of the manifold? It could be breached along with the ceramic fiber insulation and hot exhaust gas is leaking out. The hot gas would then cause the plastic manifold to melt.

The damage to the manifold appears to be external and so that is why I’m thinking there’s a leak of flue gas.
 

JamesW

TFP Expert
Mar 2, 2011
17,327
Since it's an indoor installation, the venting is going to be a critical factor. I suspect that the fire is being trapped in the combustion chamber causing everything to overheat.

I recommend that the O.P contact a qualified gas contractor to check everything.
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,214
Tucson, AZ
Since it's an indoor installation, the venting is going to be a critical factor. I suspect that the fire is being trapped in the combustion chamber causing everything to overheat.

I recommend that the O.P contact a qualified gas contractor to check everything.
100% agree. This is obviously a dangerous situation. Take the heater out of service, lock out the controls and call in a qualified contractor (HVAC and gas qualified). A malfunctioning gas heater can be very dangerous (fire hazard, carbon monoxide hazard, etc).
 

Pool Clown

In The Industry
Sep 5, 2008
2,022
Silicon Valley, CA
I think If there was some kind of an obstruction with the venting, the Stack flue switch (SFS) would trip. I believe the heater is running OK. My money is on an exhaust gas leak. You have lost the seal at the bottom edge of the combustion chamber where it meets up to the manifold. Rusted out? Or was pried on at one point, bending the sheet metal and has left a gap.

I too think you need to call a guy.
 

JamesW

TFP Expert
Mar 2, 2011
17,327
The damage does seem to be confined to the top of the manifold. So, maybe an exhaust leak.

I would think that it would have been obvious when changing the manifold, but maybe it was not noticed.

Was the heat exchanger ever replaced?

How old is the heater?
 
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Pool Clown

In The Industry
Sep 5, 2008
2,022
Silicon Valley, CA
Im a dope! thought it was the bottom. I think either the seal was not good from the factory, or like James suggests a later repair that didn't get sealed back up all the way. The older heaters just had high temp silicone smeared all over. Later versions had a silicone o ring to seal. To be honest, either could have failed. Especially If you had the silicone smear, and a subsequent repair made use of the o-ring. The mechanic may have not gotten all the old silicone off the sealing surface before he assembled, creating a weak spot in the seal. But if it happened twice? the tub or lid may be deformed or has a hole rusted. You need to look at the area thoroughly for holes before you reassemble.
 

JamesW

TFP Expert
Mar 2, 2011
17,327
Since it's indoors, the back-pressure from the extended venting will be higher than normal, which will make a leak more prominent.

There might be an issue with the venting or maybe the way wind is hitting the outside vent that is increasing the combustion chamber pressure.

Knowing the history of the heater would help.

Maybe heat trapped in the combustion chamber caused warping or a failed seal.

The stack flue sensor might have been periodically coming on and just not noticed.
 

setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
2,074
Stuart/FL
Wow! Look like the rubber seal got hot enough to melt. Don't see evidence of external heat applied so seems like it ran dry. A lot had to go wrong for that to happen. I agree with others this needs a pro to look at it. Too many potential hazards for a DIY unless you're also a qualified gas tech.

Chris
 

LSUser

Member
Dec 30, 2019
6
South Louisiana
Thank you, gentlemen.

The fan is coming on. Good suction on the intake. SFS reporting 320 F. The exhaust stack is up 6' and then 90 deg to exit the wall. Good flow of hot at the termination as well. But the pipe is only a 4". I will upgrade to 8" since the manual recommends against anything smaller than 8". I think that will go a long way toward eliminating this problem.

The heater is about 2 years old. The exchanger has not been replaced. It has been cleaned at least 3 times. My wife checks the chemicals daily. I replaced the igniter (after i broke it once while putting it back together after cleaning the exchanger, sanding and re-painting the inside of the exchanger tub before).

The metal tub around the heat exchanger had enough rust on it to potentially let hot air escape toward the manifold. I fabricated (crudely) an aluminum shield to deflect hot gases away from the top of the manifold after sanding it, treating with Rust-Stop, and re-painting the area.

The tank lid also has a new gasket in addition to the half-Rear heat shield.

I sanded down the deformed manifold and built it back up with a fiberglass kit from Autozone. Put it back together with a new manifold gasket and o-rings.

Last nite i started the heater and ran it for two hours without any leak appearing. Today i ran it for eight hours constantly and no leak occurred. But the manifold is still getting quite hot along its top edge.
I will look into getting some material which i could use to fabricate a better heat shield to locate inside the tub at the manifold end along with the ventilation improvement. I still wonder if anyone else had this problem.

Thank you: ajw22, James W, JoyfulNoise, Pool Clown and setsailsoon!
 

JamesW

TFP Expert
Mar 2, 2011
17,327
The heater is about 2 years old. The exchanger has not been replaced. It has been cleaned at least 3 times.
That's quite a bit of service for 2 years.

What's going on that you feel like you need to keep cleaning the heat exchanger?

Is there enough air supply for the heater?

Is there a condensate drain in the exhaust venting?
 
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LSUser

Member
Dec 30, 2019
6
South Louisiana
Sounds like you need a new tub and lid (#15 & #20)
Mastertemp install and user guide
page 51 and 52.
Yes sir. This one's had it. Already sanded and repainted it prior to this episode.

That's quite a bit of service for 2 years.

What's going on that you feel like you need to keep cleaning the heat exchanger?

Is there enough air supply for the heater?

Is there a condensate drain in the exhaust venting?
I opened the tub twice before this time, so i cleaned the exchanger while i was there anyway.

The heater is in an 10' x 16' room (with the filter and the pump) which has 2 - 20"x 26" openings to outside air.

My condensate drain is between the SFS and the first 90-degree bend upward, sir.
 

JamesW

TFP Expert
Mar 2, 2011
17,327
Most people never even think about opening the tub. What made you think that there was a reason to open it?
 

LSUser

Member
Dec 30, 2019
6
South Louisiana
On this particular time i opened it, the reason was because of the manifold melting. This happened before, about a year ago. The time before that (i think?) was when the SFS complained and i opened it to clean the coils. I think that is what was going on, sir.