isolating CH side from combi to identify pressure loss

[silver50]

Well good news in that I had the main heat exchanger replaced and all is well. Almost..
(incidentally was advised if keeping the boiler I change the insulation pads next year but I do only want this boiler to see me through the winter)

I've become aware tonight that when CH running code 07 lockout seems to kick in but then reverts back to normal operation after very short spells (usually within seconds). Any ideas on this? Might this just be an iffy primary thermistor in the heat exchanger? It happens just as the burner lights and starts heating.

Thanks

 

[ianmcd]

A new primary thermistor should have been fitted when the heat exchanger was replaced

 

[silver50]

Ian, do you think this happening does just sound like the sensor is going bad? I just sat and watched the boiler while filling a bath and it momentarily cut just the once for a few seconds (red light displaying 07) while getting up to HW temperature (seems to be set 45c). Seemed similar last night when the CH was on, cutting when starting to heat.
It was me who secured a new Vokera heat exchanger at a good price on ebay so I can't really blame the engineer who fitted it for me. Seems easy enough to access to pop one in now though.

 

[ianmcd]

yes it sounds like it is momentarily dropping out, I just changed one on my last job, not a difficult thing to do and they are not expensive, I actually change them on every service although there is no requirement to do it, means I can buy them in bulk and get a good deal

 

[silver50]

Thanks. Ordered one just now.

Could I fit it myself? I know I can access the thermistor ok by removing the R/H side panel. I don't know what the engineer did as far as isolating water though (when he changed my heat exchanger) but I don't think he touched the ancient valves beneath the boiler. Could I get away with taking pressure off the system, say from a radiator, and then unscrew the old thermistor catching any more water from the heat exchanger? (obviously electricity off).