Seems difficult to find a good plumber, although we are well served here. When we bought the house, September 1995, it had a coal-fired heating system. There was a gas supply to the house, but not used, so we had a new gas boiler fitted, with the necessary changes to the system, all for around £1300.
The boiler is a Potterton, gravity fed system, and is still going strong, just over 25 years later, although a little like 'Trigger's broom'.
A few years ago, the inner flue corroded, allowing some exhaust to feed back into the intake. Plumber got a flue assembly, but just replaced the inner, as the outer is cemented into the wall of course. The pressure monitoring had got upset, causing it to pop on and off erratically, and the relays had been damaged, so a new relay block was fitted.
About four years ago, some time after the flue issue, the fan motor got sticky bearings. It squeaked a lot, but also seized occasionally. I replaced the motor, but a few days later, it would start up, then run for only a few seconds, and shut down again, repeating every few minutes. A websearch found an answer, seizing motors put stress on the circuit board, requiring a new one.
A reconditioned board was available, for about £50, but delivery in 5 days, with a substantial deposit, refundable when you send the old one back.
A brand new one was available, for about £120, about 15 minute drive away. (Plumbase have a distibution centre nearby, open to retail sales.)
This was winter. So off we went, and 40 minutes later returned with the new board. Took 12 minutes to fit, all working fine again, and soon warm and toasty. Still working fine now.
Can't see the need to replace it, with a combi, with so much replumbing to be done. Any money saved in using less gas would give payback some time after I'm dead.
The gas section we must not touch, but the mechanical stuff is separate, and can be fixed without disturbing the gas.
New and fancy, not always better.
We moved to our present house 36 years ago when our 3rd child was due and there was just no way we were all going to fit into our then wee end terrace.
The new house was actually a new build, on a small estate not half a mile from where we then lived, which we put a deposit down on before they even dug the founds! The build was quite advanced for it's day with ordinary brick outside but using heat insulating blocks for the inner courses (they are very light, almost like aero chocolate bars if you can imagine) with polystyrene sheets faced with heat reflective foil on one side fixed to the cavity side of the blocks - so we still have a cavity between the outer brick and insulated blocks/polystyrene sheets so air can still circulate. A number of people on the estate took up the relatively recent "craze" to have insulating material blown into their cavities for increased insulation and some are now having problems with damp patches on interior walls. I did think about doing this, so glad now that I didn't! - It, like you, had a gravity fed Potterton Netaheat boiler system. This proved very reliable and, no doubt due largely to the insulated walls, actually cheaper to run than our old end terrace (which surprised us as the new house is detached and quite a bit bigger).
After many years of very reliable service - and being serviced by a service contract with our "big name" gas company - the boiler failed. A faulty circuit board was diagnosed and replaced. A couple of years went by and the same board failed again. It too was replaced. Then one morning I got up to go to work and realized the heating wasn't on. The boiler was cycling through it's startup procedure - Fan starts and runs. Relay clicks (which provides current to the main gas valve) gas valve opens and lights pilot which then soon ignites the main burner - The fan was running and the relay was clicking but, after a brief run of the fan it was all shutting down again before trying again in an endless attempt to get going. I turned it all off and called the emergency line before going off to work. Mid afternoon Mrs J called to say they'd been but needed a part they didn't have with them and they'd be back tomorrow so she'd put the immersion on.
It took them two days to make contact with us just to tell us there was a shortage of the part needed and they'd be in touch when they'd got one. Unfortunately it was Mrs J who had answered the call and she hadn't thought to ask what it was they were trying to get. Several days went by and Mrs J started getting very niggly (you'll all know what I mean guys?) So I rang the emergency number and got passed around a few non technical people before managing to speak to someone who could tell me that the job card reported a fan failure on my job so new fan needed and there weren't any in the country. Damn!
This news caused Mrs J to go into semi meltdown - a condition which always, in desperation to restore normality and family harmony, brings out max effort on my part! So, more so it would look like I was doing my best, I took the casing off the front of the boiler for a look see (of course I'd never touch anything to do with the gas side) and it was as I was doing this that I had a "lightening flash" moment! - Hang on, I thought, the bloody fan runs though doesn't it? how can it be the fan at fault? - So i stripped the fan out of the casing, clamped it in my garage vice, connected power (mains, cringe) to it and, standing well back, flicked the switch. Fan ran perfectly. It wasn't until later that I realized the fan motor was uninsulated so the metal vice would have been live whilst I had the power on! Luckily I didn't touch it and the bench top is wooden - someone was definitely looking out for me that day!
Now, having had no working boiler for over a week and feeling pretty annoyed, I rang the emergency line to report my belief that they had diagnosed the fault wrongly. Incredibly they wouldn't believe me and chastised me for working on a gas appliance. I demanded to speak to a "technical" person who pretty much repeated the script to me whereupon I pretty much "lost it"! The voice then said, "look sir, I can see this is very upsetting for you and this is highly irregular but, although I'm sure our engineer will have correctly diagnosed your fault, just this once I'm going to authorize a second opinion so You can expect an engineer to call this afternoon.
That afternoon the chap arrived and I showed him the fan running in my vice. he nearly had a fit, pointing out that the vice would be live, but agreed that it definitively proved the fan was absolutely fine! He reinstalled the fan and after about 5 minutes came into the living room and told us the main gas valve was stuck. Not worth trying to free it up/clean it out so new one needed - Oh dear God, here we go again, I thought. But no, "I think I've got one in the back of the van" and he had us all up and running again within about a half hour.
A few years after this Mrs J decided we really had to have a new kitchen - I couldn't see anything wrong with the old one, but have to agree that the new one does look great. Was it worth the cost though? - and part of that was to update the boiler (It was starting to play up again taking about 3 or 4 times longer to complete it's fire up procedure, I think due to the pressure switch which I could have replaced myself as it's electrical not on the gas side, but I went with the plan for a new, potentially more economic to run, installation.) Mrs J didn't want to loose the hot water tank in the airing cupboard and, after consulting my boiler friend, we settled on a condensing Worcester Bosch but not a Combi. So far, probably about 8 years or thereabouts after installation, it's going just fine and definitely using less gas although some of that is probably due to me doubling the depth of loft insulation - what a horrible job which I will never undertake again! The old Potterton must have weighed a ton. It took 3 of them to carry it out and they damaged the back door with it on the way! I noticed it's flue was, like yours, badly corroded.
It was shortly after this that I helped one of our neighbours get her car started and, chatting away as I do, mentioned our troubles. "Oh, my boyfriend's a gas engineer" she said, "you should speak to him" So, next time I saw him I did. Turns out he's a wee two man band specializing in "problems" others can't solve - a very knowledgeable chap. The outcome was I scrapped the maintenance contract and he's looked after my boiler ever since. Which reminds me it's actually due a service now.