Hi,
Am trying to understand my mother's Apollo boiler. It has an intermittent fault.
In the last couple of years, it has had a new thermocouple, a new "low" stat, and a new pump over-run switch. The RGI was not throwing parts at it, and the replacement of these has solved some problems: I think we can fairly say these new components work. We're stuck with one remaining fault in that it will sometimes turn off the pilot soon after switching off the burner and then the pilot won't stay in (i.e. the overheat stat is preventing the pilot from being on: it is a thermocouple interrupter overheat stat design).
The Apollo 30/50B has a "high" stat and a "low" stat instead of an adjustable themostat. It also senses the need for pump over-run based off casing temperature, not off heat exchange temperature, so it can be a bit hit-and-miss as to whether you get over-run or not, so it is sometimes possible to have 80+°C flow temperature without over-run. On the plus side, fault-finding is, normally, simple.
The boiler is supposed to run at 82°C maximum, but it is currently rated at around 10kW output, and TRVs mean it can sometimes find itself running 2-3kW of rads only; I have measured 86°C+ flow temperatures in this condition if the boiler is run on the "high" stat. The "low" stat switches at around 70°C.
MY QUESTIONS:
At what temperature would you expect the overheat stat to 'trip'?
Given that the boiler output is excessive for the heating load at times, would you expect the flow temperature to reach 86°C+ before the "high" control thermostat cycles the burner, or would you expect the thermostat to maintain 82ish? I'm thinking these bimetallic themostats are probably quite slow at sensing anything?
It would be nice to know what is going on. Anyone have experience of these legendar(ily bad)y boilers?
Am trying to understand my mother's Apollo boiler. It has an intermittent fault.
In the last couple of years, it has had a new thermocouple, a new "low" stat, and a new pump over-run switch. The RGI was not throwing parts at it, and the replacement of these has solved some problems: I think we can fairly say these new components work. We're stuck with one remaining fault in that it will sometimes turn off the pilot soon after switching off the burner and then the pilot won't stay in (i.e. the overheat stat is preventing the pilot from being on: it is a thermocouple interrupter overheat stat design).
The Apollo 30/50B has a "high" stat and a "low" stat instead of an adjustable themostat. It also senses the need for pump over-run based off casing temperature, not off heat exchange temperature, so it can be a bit hit-and-miss as to whether you get over-run or not, so it is sometimes possible to have 80+°C flow temperature without over-run. On the plus side, fault-finding is, normally, simple.
The boiler is supposed to run at 82°C maximum, but it is currently rated at around 10kW output, and TRVs mean it can sometimes find itself running 2-3kW of rads only; I have measured 86°C+ flow temperatures in this condition if the boiler is run on the "high" stat. The "low" stat switches at around 70°C.
MY QUESTIONS:
At what temperature would you expect the overheat stat to 'trip'?
Given that the boiler output is excessive for the heating load at times, would you expect the flow temperature to reach 86°C+ before the "high" control thermostat cycles the burner, or would you expect the thermostat to maintain 82ish? I'm thinking these bimetallic themostats are probably quite slow at sensing anything?
It would be nice to know what is going on. Anyone have experience of these legendar(ily bad)y boilers?