Mike4 wrote:SO MANY points in this to cover!
Thanks for taking them on!
Yes they could be related, but not necessarily. More details about the exact nature of the intermittent HW will reveal. Is it random, i.e. does it work fine for some showers, but not others? Or does the water cycle up and down in temp? How long is the cycle?
It cycles up and down.
In the past, it would go up, then down, then up again and stay up. That's something I've encountered in many places and can live with on the basis that getting it fixed is *somewhere* on the to-do list. And for a decent spell it stopped doing even that, or maybe I just didn't notice it over the summer when even shower-cold isn't uncomfortable.
The recent behaviour that's harder to live with is when it rises very, very slowly to tepid then falls back to freezing a couple of times, then stays on freezing longer than I can wait.
Whether or not you can see/find the leak, we know every litre of water you add to get the pressure back up is coming back out of the system somewhere, or the pressure could not be dropping repeatedly. Unless you have a radiator acting like a tank and blowing up like a balloon!
Adding water repeatedly supports internal corrosion creating sludge so yes the two faults could be related. Your boiler has two heat exchangers. Sludge gets deposited in the domestic hot water heat exchanger, preventing transfer of heat into the domestic water leading to the gas HE overheating and the software turning the gas flames first down, then off. Then it all cools down and the software starts the cycle again.
Indeed, my attempts to educate myself found a good youtube explanation of that from a plumber in (I think) the Portsmouth area. He spoke of several possible causes and showed many pics of cases he's dealt with.
I was trying to see how well the pressure holds when I keep the heating turned off. But that's thwarted by the hot water now depending on it!
The plumber's comment about the burner going ON and OFF when heating the rads is interesting, this should modulate down on the Combi 80 ECO rather than turn on and off. This is a third fault but could explain the HW fault, depending on the answer to my question about the HW behaviour above.
It's something we both observed, and consistent with the "old" hot/cold cycle. Some part of it (probably the heat exchanger as you say) being gunged up was his explanation. At the time my intention was to live with it until summer and (hopefully) the heat pump.
I don't know how he knows your boiler is "running inefficiently". Did his gas analyser tell him this? What did he mean by "inefficiently" anyway? Did he state the percentage efficiency perhaps? Or did he just mean "it doesn't seem to be working very well"?
I think it was more that a new boiler would run more efficiently. Being more modern, not cycling up and down, not having these infirmities of age.
Carbon monoxide should not be a problem you need to worry about as the Combi is 'room sealed", meaning it only communicates with outside air. So even if it was running like a dog and producing CO in spades it would not be escaping into your living environment. Did he measure the CO it produces? What was the value?
I thought your HW problem had been going on much longer than the recent cold snap....
He explained that about the CO too. My initial concern was when I fired up the heating and got some smells in there, which I thought were *probably* just general gunge getting disturbed by running it. Or even traffic fumes from something particularly noxious outside in the weather inversion conditions that also created the cold snap. He measured the CO both inside and outside the flue, and those at least were fine.
