LAARS EBP-175 Strange Behavior

nikolay23

I have LAARS EBP-175 and when there is a request for hot water (shower or laundry) the boilers starts up at about 168 as expected. The temperature on the display normally goes up to 173,178,180,185 & 190 in about 10-15 seconds. At 190 it shuts off. Then the display temperature gradually starts going down and the boiler starts up again at 168. The same continues multiple times as long as there is a request for hot water. The hot water is being provided without any issues. I tested to see if the same happens with heat and it is NOT. Any suggestions are greatly appreciated. Thank you.

Tom_133

My assumption is whatever tells the boiler to make heat, maybe a relay box, is not telling the boiler to fire for heat. I would check there first. Figure out what calls the boiler to come on for heat and make sure its working.

Jamie Hall

Um... well, I haven't worked on these things, but reading the manuals and the description, it sounds to me as though it is firing just fine on a call for heat, but ramping up to the high limit and shutting off. Then dropping back to the low limit and repeating. And, off hand, I can see two possible scenarios which will do that -- either not enough hot water demand for the modulation to match (somewhere around 2 to 3 gpm), or the modulation not working.

nikolay23

Thanks for the feedback. I am kind of suspecting "heat exchanger, flat plate" to be some kind of problem here. From what I understand this part passes domestic water once the call is made. Maybe it is partially clogged not providing full demand.

bgard

How old is this boiler? Is the jacket blue or grey?
It sounds like the plate heat exchanger is not removing the heat from the boiler water fast enough. Circulate white vinegar through the domestic side of the heat exchanger for a couple of hours to remove scale

nikolay23

The boiker is 13 years old. It has a blue jacket.

Zman

bgard said:

How old is this boiler? Is the jacket blue or grey?

It sounds like the plate heat exchanger is not removing the heat from the boiler water fast enough. Circulate white vinegar through the domestic side of the heat exchanger for a couple of hours to remove scale

If the problem described is happening at full flow, I would agree with this.

bgard

That boiler has some test pins force high or low firing rate they should not have any jumpers on them, there are four brass pins on the lower left corner of the circuit board marked hi low and mod they should not have any jumpers on them if hi is jumped the boiler will always run at hi fire

nikolay23

Thanks. I am working with someone suggested by LAARS and he suspects it is a plate heat exchange part that is causing all of this.

Tom_133

Man I must have read the initial post wrong. I thought he said his hot water was fine, and that the heat wasn't coming on. Strange

hot_rod

And it is also possible the boiler side of the DHW heat exchanger is partially plugged. I saw this recently on a fairly new Viessmann Combi boiler. It presented as a plugged or blocked DHW side of the HX, when disassembled it was actually the "A" side that was partially plugged causing the lockout condition.

nikolay23

I had new DHW heat exchanger installed, but the unit still keeps short-cycling on domestic hot water call. It does produce hot water without any issues. Not sure what else to try. The machine has new main burner chamber, new circulation pump, new anti-condensing valve, new temperature sensors and new DHW heat exchanger. I had a spare control board and tried that as well.