Ravenheat 820 hot water cuts out

[Agile]

Regarding those above who suggested checking temperature sensors on this boiler. Where are they located ???

I thought this boiler only used step modulation controlled by a double action thermostat on the front panel knob?

Tony Glazier

 

[chrishutt]

Yes, you're more or less right Tony.

The boiler flow pipe has two thermostat probes (volatile liquid type) attached, one for CH (2 stage hi/low) and the other for DHW (which controls mod. coil). The main heat exchanger (which is also the DHW heat exchanger - four pipe type) also has an overheat cut-out in thermocouple circuit and an electrical high limit thermostat which will shut down gas valve and fan (to low speed).

In DHW mode the pump sends boiler primary water around internally, enveloping the DHW heat exchanger tubes within the main heat exchanger. The DHW stat will open or shut modulator coil (but not actually modulate!) so producing high or low flame to maintain heat exchanger temp. and therefore DHW temp. However if temp. rises too high the high limit stat will shut down burner completely.