Strange condensing/ modulating operation after LP fill up

marsfromrexford

Good morning all, I finally was able pin down a pattern of erratic boiler operation on my hydronic system that is directly related to LP delivery. Basically the furnace seems to run rough for about a day after the LP deliver and this pattern has been consistent from day 1 of the install or since my very first fuel delivery. It seems like the furnace can't turn down with out 'losing flame' error code 78 flashing. before flame loss the flame turns completely yellow. The furnace short cycles and the boiler primary loop temperature spikes to very high temps where normally the primary loop temp runs between 130-160 based on outside temp. Since noticing the pattern I bought a cheap amazon digital manometer that measures pressure in WC. standing WC is about 11 at a drip leg just before the furnace. When the furnace lights the WC drops within 5-10 seconds to about 3.5 to 4 WC. The specs on the furnace call for 13-8 WC / LP. The cook top range drops the running pressure about about -2 WC with all burns running at max. There is only one regulator at the tank that goes to 1/2 or so copper about 10ft to my house to where it transitions to 1" black through about 25ft to furnace. I did mess with the regulator; adjuster. I tightened an adjuster down about one turn and it seemed to help, raised the static pressure to about 12WC and seems to prevent some of the drop of WC but was still falling below causing poor running. After a day passes everything seems to go back to normal.

Sorry for long question and thanks in advance for taking a look.

Mario

EBEBRATT-Ed

You could have a bad or sticking regulator, moisture in the fuel etc. You said a regulator at the tank, don't you have another one before it enters the house? That is the usual set up.

You could also have undersized pipe.

marsfromrexford

The manufacturer of the regulator suggests using the one valve setup when 'the' appliance is on the same exterior wall as the entry point of the line. All other applications show tank valve and house valve separately. I suspect that my valve is undersized or having a lacking of proper valves but don't understand why filling the tank affects it for a day.

Thanks!

mattmia2

Perhaps liquid propane is getting in the regulator when the tank is full and it isn't regulating properly until it is seeing all vapor?

JUGHNE

Or the filling of the tank increases the pressure to the regulator drastically and it takes some time to recover.

IMO, you need two regulators, one at tank and one at house. The standard set up.

EBEBRATT-Ed

the op said the pressure drops from 11" static to 3.5-4" when the boiler lights.

All he needs to do is find out why. With only one reg at the tank I would contact the propane supplier,Show them what is happening

yellowdog

i would guess the 1/2" copper line is your issue. did you recently change fuel providers? almost sounds like someone took a 1st stage 2nd stage setup and changed it to a twin stage regulator and just ran copper to the house where the old 2nd stage regulator was. call your propane provider and make them fix it.

marsfromrexford

Thanks guys, how much drop in pressure should there normally be or is acceptable from static to running?

Thanks,
Mario

mattmia2

Does the pressure still drop when the boiler fires after some of the tank has been consumed?

The drop will depend on the regulator and the engineering of the piping but it shouldn't fall below the minimum on the ratings plate of the boiler.

EBEBRATT-Ed

Your supposed to maintain 10" or the minimum pressure on the boiler nameplate.


The pressure drop from the last regulator to the appliances with everything running should not exceed .5" of wc.

marsfromrexford

.5 inches - wow, that's quite a bite different than my conditions

The condition dissipates after 1 or 2 days after LP delivery and the amount of the fill up dosen't seem to have affect. The tank was at 25% before and 70% after delivery, The tank has been filled to 90% and still has the same affect.

Thanks guys so much
Mario

Solid_Fuel_Man

After a few days and all is "running normal" what does you manometer tell you? 

I agree, a twin stage regualtor at the tank and 1/2 copper won't flow much LP. I don't have my book handy, but I think 10' of 1/2 copper is only good for maybe 80,000 btu. 

The right way to do this is check pressure at the regulator static and dynamic, and compare that with what you are seeing at the appliance. 

Pressure is usually set at 11-13" static (lockup pressure) and piping sized for 10+" with the entire system under max load. Appliance minimum pressure must be maintained or else soot and CO will be produced. 

It does sound like someone remove a 1st and 2nd stage regualtor and installed a twin stage and reused the copper. 

marsfromrexford

I couldn't help but notice a bit of skepticism on your part with my stance that all is fine once the tank level lowers. If my intuition about your skepticism is correct than you are also correct. The running inches of WC still drops to 6-7 now, not all the way down to 3.5-4 as before. I called my supplier, they told me my running pressure was 12.5 which is impossible because non of my appliances were run or able to run when the gas service was installed and 'tested". I didn't commission the boiler until the gas company left because there are several steps to take and I didn't want to hold him up.

Solid_Fuel_Man

You need 2 regulators. And likely a Maxitrol 2psi system inside with a regualtor at each appliance, or properly sized low pressure repiping. 

This isn't rocket science. Pressure drops due to too small of piping. You need more pressure (where possible and legal) and larger piping.