Heater Booms and Fails to Light--an unusual cause

Hayward H-series Heater

A couple of weeks ago I ran across a Hayward H-series heater (atmospheric, not low NOx) that failed to light. It would go through its start-up sequence: It activated the spark igniter and opened the gas valve and then fail to light. A couple of times it lit with a boom and then just as quickly the flame went out.

Orifice blocked by spider web next
to open (good) orifice

Usually this indicates that spiders have built webs that block the tiny orifice that supplies gas to the burners. When the orifice for the burner that is under the igniter is clogged, the heater often fails to light. Occasionally, enough gas from the other burners will build up in a cloud and drift over towards the igniter. In this case, it lights with a boom.  

Burner with openings blocked by rust

But today, that was not the problem. As the picture shows, rust deposits have built up on the burner and are blocking the openings. The rust was particularly bad on the burner that is under the igniter.

The rust came about because the heater is "condensing." This happens when condensation forms on the heat exchanger (located directly over the burners). The condensation then drips down onto the burners. You can often hear the effects of a condensing heater. It will sound like water being flicked onto a hot skillet.

The way to fix the problem is to replace both bypass valves in the inlet/outlet header. There is one bypass that operates on pressure and one that relates to temperature. Either could cause this problem and since it takes a good deal of labor to get in there, it is better to replace both. Then, after fixing the cause, fix the damage by replacing as many burners as necessary.