warm feelings

My central heating system and I have come to know each other quite well over the 15 years we have been together. At first, our relationship was rather distant, but over the years I feel we have become friends.
In the early years, whenever the house was at the wrong temperature, we would be in conflict. "Winter again and the heating is on the blink; if only we had had a descent heating system installed by someone competent,..." etc. I even resorted, in this early phase, to bringing in "experts", who would wave their magic spanners, replace a part or two and leave me with warm accommodation and a hefty bill, but I eventually learnt my lesson and decided to apply my engineering brain to the problem of simple binary logic, albeit operating at 240V.
In these early years the problems were due to component infant-failures, to earlier poor maintenance and, frankly, to a barely adequate installation. I must be fair on the installer here and point out that the boiler was added to two, combined heating circuits that had been cobbled together by the house's previous owner. The boiler fitted is a Glowworm condensing boiler, and it is the heating element in an otherwise conventional fully pumped, unpressurised system. Such installations are required, by the manufacturer's rules, to include a bypass circuit to accept the overpressure from the pump in the event that all the heating circuit parallel radiator valves are turned off. The fitted circuit, being a little short (i.e. low in copper content) has always made the boiler short-cycle, which is not an efficient mode for a condensing boiler.
Over our years together I have corrected a number of amusing failures, but left this bypass circuit alone. I have replaced the flue fan unit, the over-temperature cut-off thermostat, the hot water thermostat, the pump and the motorised valve, this latter item, several times. I have also cleaned the burner and the main boiler circuit board which, over time, accumulates enough conductive dust to prevent the effective operation of the flame ignition (there being no pilot light). I have even rebuilt a couple of valve motors from the working components of multiple failed units to correct burnt out resistors and failing micro-switches, but unfortunately Honeywell have now changed the design subtly, and the new parts and the old no-longer fully interwork.
In order to avoid doing repairs in bad weather I have also run the heating for extended periods with string holding the 2-way valve manual override active or with the heating on continuously so that the pump ran 24/7, since it had lost the will to start itself, once it had stopped.
The reason I claim that the heating system is getting to know me, as well as the converse, is that last winter it worked trouble free throughout the coldest spell of weather, when I was at my busiest doing other things, whereas in previous years, it would have taken such opportunities to break down on me.
Knowing that some amount of maintenance was going to be essential this year, I ran the heating with the temperature still positively balmy outdoors, I listened carefully to all the components, ran my hand over all of the pipes and determined that the only problems this year, to add to the ongoing fault in one of the pump isolation valves, that necessitates the partial draining of the system in order to do any pump maintenance work, were:

1. The pump, in addition to not wanting to start, did not run reliably.
2. The boiler did not reliably light.
3. The 2-way valve had something wrong, because it did not return to central when the heating demand was off.
4. The programmer's back-up battery was shagged, allowing it to forget any programming information if it lost power for ten or more seconds.

I was forced to conclude at this point that the only reason the system had delivered hot water all summer to the cylinder was that it had been successfully operating a convection circuit, and that the default, twice a day programme had masked the occasional failure of the boiler to light.
So I ordered a new pump and, while I was admiring Screfix's online site, I noticed, while searching for valves, that they had a reasonably priced bypass valve for my ever leaky bypass circuit. These items arrived swiftly and, while all was disassembled I had time to clean the circuit board in the boiler, diagnose the 2-way valve problem (mechanism worn out beyond repair) and determine the type of the back-up battery in the Honeywell programmer. I ordered the valve motor (and a valve, the price was essentially the same with as without) from someone on ebay. The battery was harder to source, because the original was obselete, a Varta V110H. I found a company called Cell Pack Solutions on the web, but their website said a replacement cell, a 1V150H, was out of stock and to call. I called on the Monday and explained my problems. They were willing, for under a fiver (5 pounds sterling) to get a compatible cell out of stock, attach the required 3 pins to it, package it, post it and accept a credit card; an excellent and polite service.
So now, with all of these parts fitted and commissioned I have a warm feeling about my relationship with my heating system, although I am realistic. I know it could all break down again soon.
Incidentally, in these cost and carbon dioxide conscious times, I also bought us a joint present of a programmable room thermostat, but I haven't got around to fitting that yet, I let the rest of the components get to know each other first.