Hi all. Wonder if anyone can suss this one?
I have an old Thorn Apollo boiler, in a system with 2 heating-zones, with Honeywell 2-ways and roomstats and a hotwater zone with Honeywell 2-way and cylinder-stat. No programmer or clocks. Only using HW now, of course. Replaced the overrun stat a year ago when it got down to about 10 second overrun, allowing some minor noise at shutdown. It's been happy at 2-3 minutes ever since and all quiet. No problems till this month, when the boiler started to kettle and pipes bang loudly, always at the same temp - I have a clip-on thermometer on the boiler output-pipe - of 55C. The noise lasts for just a few seconds, but it's quite scary!
Today, I checked the system when it fired up and as the dreaded temp. approached, went to the airing-cupboard to check for bangs there. I was touching the pump, which was running quietly, when I felt it stop. There was rattling and banging from the pipework, the pump came back on and all was quiet again. Normal boiler-cycling, heat-up and overrun followed. The pump was off for about 5 seconds. So I think I've found the fault, but not the cause!
The basic circuit-diagram suggest that it could only be the cyl-stat, but why would it lose contact for a few seconds and always at the same temp?
Any suggestions will be very welcome, so thanks in advance.
Raymundo
I have an old Thorn Apollo boiler, in a system with 2 heating-zones, with Honeywell 2-ways and roomstats and a hotwater zone with Honeywell 2-way and cylinder-stat. No programmer or clocks. Only using HW now, of course. Replaced the overrun stat a year ago when it got down to about 10 second overrun, allowing some minor noise at shutdown. It's been happy at 2-3 minutes ever since and all quiet. No problems till this month, when the boiler started to kettle and pipes bang loudly, always at the same temp - I have a clip-on thermometer on the boiler output-pipe - of 55C. The noise lasts for just a few seconds, but it's quite scary!
Today, I checked the system when it fired up and as the dreaded temp. approached, went to the airing-cupboard to check for bangs there. I was touching the pump, which was running quietly, when I felt it stop. There was rattling and banging from the pipework, the pump came back on and all was quiet again. Normal boiler-cycling, heat-up and overrun followed. The pump was off for about 5 seconds. So I think I've found the fault, but not the cause!
The basic circuit-diagram suggest that it could only be the cyl-stat, but why would it lose contact for a few seconds and always at the same temp?
Any suggestions will be very welcome, so thanks in advance.
Raymundo