Laars Endurance EBP 100 combi - Intermittent F4 error with banging pipes and pressure gauge jumping

Chris Alonzo

I have a 10-year-old Laars Endurance EBP 100 combi. I am getting an intermittent F4 error. This is accompanied by a banging noise and the pressure gauge jumping up and down. I turn the unit off and on and the problem goes away. I have tested the sensor with an ohm meter and it tested good (1.4K ohms). I am wondering if the sensor is only failing when it gets hot inside the unit and would a bad sensor cause the pressure to go up and down?

EdTheHeaterMan

The Endurance is a coil raped around the combustion chamber. There is a very small amount of water very close to the flame. The pressure fluctuation is most likely the water boiling in the heat exchanger. The water should never get that hot. There is something that is not being regulated properly. the flame is too large, or the water is not moving fast enough in the heat exchanger coil or both.

If the wiring to the supply sensor from the control looks good, sometimes just removing ythe plug from the board and plugging it back in will refresh the connection. otherwise the resistance changes with temperature. If the resistance does not match the temperature of the sensor, then the control CPU (the brains) is not getting the correct information and you will get an error code. F4 as you know is the supply sensor error. Since that is less expensive, I would replace that first. The only other reason for the error is a bad control board.

Chris Alonzo

Thanks for the quick reply. I am a home owner with basic plumbing and electrical skill. But I assume that this may be something that requires special equipment to test?

Chris Alonzo

I was able to check the amps if the motor. It was 1.4A.  But the label on the motor I think says it should be 0.74A.  See below. Am I reading this right?

EdTheHeaterMan

That may be the problem. You can try cleaning the pump housing and impeller. that involves draining the boiler to access the interior (water Side) of the pump. You could also try replacing the capacitor https://www.amazon.com/MECCANIXITY-CBB60-Capacitor-Cylinder-Compressor/dp/B09BQLZF65/ref=sr_1_7?crid=3KHLZ8UXT9GMI&keywords=10uf+/180+capacitor&qid=1673804672&sprefix=10uf+/180+capacitor,aps,168&sr=8-7

That much amperage (almost double) tells me that pump is not at its best If you want to go for the whole pump, it is in stock at Supplyhouse.com https://www.supplyhouse.com/Laars-2400-005-UP15-42F-Circulator-Pump-1-25-HP-115-volt

Chris Alonzo

Thanks. The weird thing is that I double checked it today, and the amps were normal, yet the problem still exists.

Is it also possible that the source sensor is giving a false temperature reading,  and the flame is staying on too long, causing it to boil?

Chris Alonzo

I found out that the voltage was dropping to the pump. It started at 120V, then dropped to 54V, then to 14V, all while the pump led was on and flame was firing. 

Is the pump modulated? Or should it be at 120V all the time?  If it is modulated, would you expect a faulty PWM board? Or is it it a faulty boiler control, which is no longer available?

miodowski1973

Well I have had this same issue. And turns out it was the boiler control. Aka the board that has the screen if anyone else is having this issue. I've have ran down a bunch of rabbit holes with this furnace. I've have 6 of these units still going. So I have a PhD in this old furnace if anyone has any issues. Please comment I'll help

Chris Alonzo

I thought I had updated this thread. Yes, It was the boiler control, which has been discontinued.  Fortunately, I realized that it only happened after running for a while. If I let the boiler cool down for a while, it woukd start working again. So, I unscrewed the board abd let it hang outside the cabinet to keep it cool. It has been working ever since.