Glow Worm 38cxi ignores hot water control

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If you set the hot water temperature to zero on the front panel control the hot water system never comes on. If you turn the control to the very minimum setting that will make the hot water circuit active, the burner lights and the hot water output temperature quickly rises to 65C (maximum). It doesn't seem to matter where the front panel control is set, the hot water is at maximum temperature.

I removed and checked the 10k potentiometer on the temperature control and it seems perfectly OK.

There is plenty of water flow on the hot water output and this is a very soft water area so it isn't likely to be a blocked dhw heat exchanger. I've already replaced the hot water output thermistor.

Any ideas where I should look next
 
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It appears the preheat function is on when it should be off at DHW setting between 0 and first icon.
I would suggest (if you havn't already) to reset the boiler.
Turn the mains reset switch to 0, wait for 5 seconds, turn mains reset switch to 1, the boiler is reset.
 
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It appears the preheat function is on when it should be off at DHW setting 0.
I would suggest (if you havn't already) to reset the boiler.
Turn the mains reset switch to 0, wait for 5 seconds, turn mains reset switch to 1, the boiler is reset.
I can't see how the pre-heat cycle is part of this problem.
The problem is that the hot water runs at maximum temperature (and continues at maximum as long as water is flowing) whatever position the temperature control is set to. As for resetting, the boiler has been on and off several times during troubleshooting (from mains isolation and the front panel switch).
 
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Either divertor issue /partly blocked plate heat exchanger or pcb is playing up especially if it’s old iris board.
Hope this helps
 
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The diverter valve was changed out 18 months ago as well as the flow sensor.

Are you suggesting that the plate heat exchanger is part-blocked on the dhw side or the recirculating side? We have very soft water in this region so it's unlikely to be limescale.
 
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If the hw is up to temp and you’ve test sensors take plate out and have a look, it won’t be nothing to do with lime scale it be a bit of dirt on heating circuit
 
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That is how it works, here is a link to the user instructions read the bit about HW and pre heat and the different settings .

https://www.glow-worm.co.uk/glow-worm/cxi-range-157150.pdf
On the faulty system it doesn't seem to matter where you set the dial, you get water at 65C. The only position where the water isn't at scalding temperature is 0 where you get cold water. Even if I reset the system whenever I change the setting, it still behaves the same.

I suspect that of the trouble was the plate heat exchanger I would be getting F14 (HE flow temp over 95C ) fault coming up all the time.
 
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On the faulty system it doesn't seem to matter where you set the dial, you get water at 65C. The only position where the water isn't at scalding temperature is 0 where you get cold water. Even if I reset the system whenever I change the setting, it still behaves the same.

I suspect that of the trouble was the plate heat exchanger I would be getting F14 (HE flow temp over 95C ) fault coming up all the time.
Wrong just take the advice ;)
 
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Try running two taps at the same time and see if the boiler modulates (you should hear the fan speed change) failing that have the fan setting checked by an rgi.
 
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???

OK you got me, I was lying about the water temperature and the control position. Your mystical powers of remote temperature sensing are incredible.[/QUOTE)
No you imbecile why would you expect F14 fault for blocked heat plate when I've probably seen 50 -100 of blocked plates with no fault code ;).
 
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