Brand new Pentair MasterTemp 250 LP won't ignite

Martian

Member
May 17, 2020
15
Ecuador
I have Pentair MasterTemp 250 Liquid Propane version recently installed.

mastertemp.jpg

Connected to a standard LP bottle with 30ft (10m) hose thru domestic gas regulator (works good for gas cooktops, water heater etc.)

system.jpg

Here is the regulator specs:

regulator.jpg

When heater starts I can hear some solenoid clicks inside the gas valve and ignition LED is on. It tries to ignite for 3 times and then stops. At each try I can smell a little bit gas and then nothing.
After three unsuccessful attempts to ignite Fenwall diagnostic LED blinks 3 times (ignition lockout). No other diagnostic LED's were lit (AGS, AFS, SFS, HLS, PS...)
Blower works fine. Gas control switch in ON position. No problems with water pressure as it tries to ignite so I think it's gas pressure/flow related.

User guide is not clear about the gas pressure for LP version but later I found this label somewhere inside:

MasterTemp-Info.jpg
 

JamesW

TFP Expert
Mar 2, 2011
19,372
The gas line is too small. It needs to be at least 3/4" inside diameter.

The regulator needs to be able to do about 5 kg/hr. So, that looks undersized as well.

28 millibars is about 11.2" w.c. So, that looks ok.

What is the power supply voltage?

The voltage selector plug that comes in the default configuration is 240 volts.

Did you use the correct voltage selector plug?

What size is the L.P bottle?

Unless it's really big, it's going to run out of gas quickly and it's likely to frost over.

Propane is a liquid in the bottle with vapor on the top.

As the vapor is used, the liquid needs to boil to create more vapor.

For the liquid to boil, the liquid needs to absorb heat from the tank wall, which gets heat from the air.

If there is insufficient liquid in contact with the wall, the liquid won't boil fast enough to keep up with the heater's demand.

You typically don't want to fill more than 80% or go below 20%.

So, your useful volume is about 60%.

For example, a 100 gallon bottle is useful for about 60 gallons.

At 2.75 gallons per hour, you can run the heater for about 22 hours on a 100 gallon tank.
 
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Martian

Member
May 17, 2020
15
Ecuador
Standard gas hose for the LP.

Everything works fine. Display, LED's, buttons, blower. I don't have any problems with electricity. Yes it's wired for the 240V.
 

Martian

Member
May 17, 2020
15
Ecuador
Will try to find a more powerful regulator. But hose it standard size. All regulators will have the same hose diameter even industrial ones.
I think hose diameter is not a problem as I always can supply more gas pressure.
MasterTemp gas inlet size is 3/4'' but I think it's the same size for all models.
 

JamesW

TFP Expert
Mar 2, 2011
19,372
You need the right regulator that can control the inlet pressure and is rated for more than 5 kg/hr.

The gas line needs to be 3/4" minimum.

The inlet pressure and pipe size need to be right or you can have serious problems.

If you have any doubt, consult a professional gas contractor.
 

JamesW

TFP Expert
Mar 2, 2011
19,372
Heater uses 250,000 btu per hour.

1kg = 46,450 btu.

250,000 ÷ 46,450 = 5.4 kg/hr.

Note that the maximum inlet pressure is listed as 14" w.c. You can't increase the pressure higher than that to compensate for an undersized line.

Providing more than the 14" w.c is dangerous and it could damage the heater.

Anything less than 3/4" line is going to result in inadequate gas supply and the heater could be damaged.
 
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Pool Clown

In The Industry
Sep 5, 2008
2,127
Silicon Valley, CA
I agree with the supply being too small. You may want to also check the ignitor. Over the years, i have had several that have were broken right out of the box probably from a rough shipment.
 
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Martian

Member
May 17, 2020
15
Ecuador
The problem is I cannot supply a bigger hose because even gas bottle direct valve has this size. There is no 3/4" supply even from the 5ft tall bottle.

I have Takagi gas home water heater 199000 BTU max and it also has 3/4'' gas supply. Connected the same way as my pool gas heater and it just works fine.
As I can see from my Pentair specs it needs:
Maximum inlet gas pressure: 14'' wc
Minimum inlet gas pressure: 4'' wc
And this is from my home water heater (even higher):
waterheater.png

BTW today I've got new more powerful variable regulator. Still cannot ignite but can hear some scratching/cracking when it tries to ignite (as I understand).
 

JamesW

TFP Expert
Mar 2, 2011
19,372
What is the rating of the regulator?

From the regulator, it needs to be 3/4" inside diameter.

Check the gas pressure at the inlet pressure tap before the heater tries to fire and watch as it tries to fire.

Check the resistance of the igniter.
 

Martian

Member
May 17, 2020
15
Ecuador
Got this thing ignited covering 2/3 of the intake air with 3kg/h regulator:

IMG_2810.JPG

Tried this variable regulator from 4 to 8 kg/h but even on the lower position it won't let gas to get out:

IMG_2742.JPG

Finally I've got fixed 3kg/h regulator which doesn't lock intake gas valve but doesn't ignite also (but I can smell the gas as it tries, with more powerful regulators it won't smell).
Covered 2/3 of the air intake and it worked. Tried to run for about 20 mins and it works like a charm. Now I have another question: is it safe?

Maybe there is another way to fine tune intake gas valve without covering air intake?

IMG_2811.JPG
 

JamesW

TFP Expert
Mar 2, 2011
19,372
You need a regulator that can provide the correct gas pressure and volume.

You're modifying things in unsafe ways.

You need the correct size pipe from the regulator to the heater.

If you can't get the right regulator and pipe, you should not use the heater.
 

Martian

Member
May 17, 2020
15
Ecuador
As I wrote before all regulators here will have the same hose size.

As I wrote also if I use more powerful regulator with 4kg/h or more intake gas valve just locks and doesn't let gas to get out.

If you can't get the right regulator and pipe, you should not use the heater.
Not an option. Now I know it can work with less air. So the solution can be another gas valve or another regulator placed just right on the gas inlet at the end of the hose instead of at the cylinder at the beginning.
 

JamesW

TFP Expert
Mar 2, 2011
19,372
You should verify that the gas pressure at the inlet is within the specs as shown on the heater label.

The gas pressure should be within spec before the heater fires (static pressure) and it should be within spec during operation (dynamic pressure).
 

Martian

Member
May 17, 2020
15
Ecuador
I think my solution is to send gas at full pressure over the hose and connect it to a regulator with 3/4'' output right one the heater.
Now which regulator? Any links to online stores?
 

Pool Clown

In The Industry
Sep 5, 2008
2,127
Silicon Valley, CA
Have you checked the orifice in the union (just above the blower)? I know your service sticker says that it is a Propane heater, but that only means that there is (supposed to be) the correct orifice in there. It would not be impossible to have the wrong orifice installed from the factory. The only difference between Gas and Propane is that orifice. IOW, You can go back and forth between a gas and a propane heater just by replacing that orifice. It should have a letter or two stamped on it. I apologize but i cant remember the correct one you should have for a 250. Im sure someone here can fill in the gaps.