Hi all,
Sorry for the epic post.
I have a Halstead Ace High combi boiler, around 10 years old and in pretty good condition; the rest of the system probably less so.
The CH has always been reliable. Recently I have been having intermittent problems with the DHW. When it works, the DHW works well and can heat a large flow rate (shower) to a good temperature. When it doesn't work, the symptoms are:
1) DHW sometimes fails to respond to demand. This can persist for many minutes, but it self corrects eventually.
2) DHW sometimes responds to demand but shuts off after a minute or so.
3) Boiler sometimes fires randomly for a few seconds, but I can find no mention of preheat in the installation/maintenance manual and there is no preheat control on the front panel.
4) Very occasionally, the boiler kettles and vents steam after a long DHW draw off.
I have looked at the following:
1) Secondary heat exchanger. I have removed this a couple of times and flushed it out. The first time I found a 1-inch nail (this was obviously a proper high-quality installation job) and a very small amount of black flaky scale. The hot side of the exchanger is coated with a thin layer of sooty black material that mostly wipes off, but doesn't flush out with water. There doesn't seem to be anything in there that significantly reduces the flow though.
2) Thermistors. I haven't managed to find a reliable spec for the thermistors, but both are giving around 16k when cold (whole diverter cooled to mains temp by running HW with boiler off) and well under 10k when hot. I haven't tried swapping or replacing these.
3) Flow switches. Both flow switches appear to be fine. DHW demand reliably gives 0V across DHW switch terminals on PCB. Primary flow switch reliably closes when the pump comes on.
4) Wiring. Opening the control panel seems to cure problems with failing to respond to DHW demand. I suspected a bad connection in the low voltage loom, but I have had the loom out and wiggled it around a lot with a meter on it and haven't been able to find any continuity issues.
Other things:
The DHW pump overrun is only 3 or 4 seconds. Is this a fault? The overrun time is not specified in the manual. Explains the kettling perhaps?
I can't reproduce any of the faults with the control panel open, which is incredibly frustrating.
Thanks for any advice.
Sorry for the epic post.
I have a Halstead Ace High combi boiler, around 10 years old and in pretty good condition; the rest of the system probably less so.
The CH has always been reliable. Recently I have been having intermittent problems with the DHW. When it works, the DHW works well and can heat a large flow rate (shower) to a good temperature. When it doesn't work, the symptoms are:
1) DHW sometimes fails to respond to demand. This can persist for many minutes, but it self corrects eventually.
2) DHW sometimes responds to demand but shuts off after a minute or so.
3) Boiler sometimes fires randomly for a few seconds, but I can find no mention of preheat in the installation/maintenance manual and there is no preheat control on the front panel.
4) Very occasionally, the boiler kettles and vents steam after a long DHW draw off.
I have looked at the following:
1) Secondary heat exchanger. I have removed this a couple of times and flushed it out. The first time I found a 1-inch nail (this was obviously a proper high-quality installation job) and a very small amount of black flaky scale. The hot side of the exchanger is coated with a thin layer of sooty black material that mostly wipes off, but doesn't flush out with water. There doesn't seem to be anything in there that significantly reduces the flow though.
2) Thermistors. I haven't managed to find a reliable spec for the thermistors, but both are giving around 16k when cold (whole diverter cooled to mains temp by running HW with boiler off) and well under 10k when hot. I haven't tried swapping or replacing these.
3) Flow switches. Both flow switches appear to be fine. DHW demand reliably gives 0V across DHW switch terminals on PCB. Primary flow switch reliably closes when the pump comes on.
4) Wiring. Opening the control panel seems to cure problems with failing to respond to DHW demand. I suspected a bad connection in the low voltage loom, but I have had the loom out and wiggled it around a lot with a meter on it and haven't been able to find any continuity issues.
Other things:
The DHW pump overrun is only 3 or 4 seconds. Is this a fault? The overrun time is not specified in the manual. Explains the kettling perhaps?
I can't reproduce any of the faults with the control panel open, which is incredibly frustrating.
Thanks for any advice.
