I have received so much help in this group over time that it may well be time for a bit of pay back. Because I feel less competent than many to comment on specific questions, I think I could contribute an experience report on my recent fitting of a new combi system. Some of you looking at a similar job may find it helpful, others may have a laugh on me for the mistakes that I made. Here we go:
The situation: bought a victorian 4-bed terrace in Yorkshire with a really old gas boiler (estimates put it at between 20 and 30 years) serving a hot water tank in a bedroom (!). No roomstat led to the boiler being on all the time. Plus, the attic bedroom did not have a radiator, arguably because the ch pump was so weak that it would have had a hard time serving it. The shower is one of those victorian retro showers.
We wanted a combi as we have seen combis work efficiently in other houses here and abroad. We realised the potential problems with the flow rate @35 but since we prefer showers over baths, the specific advantages of a tank system were a bit lost on us. Also, we really needed this bedroom to be free of the tank, so a major replumbing job was kind of unavoidable.
We asked for three different quotes: local small plumber (quote for
3200), local large plumber (quote for 4000), British Gas (quote for 6000). We let the plumbers decide on how many radiators needed replacing as some of the radiators are indeed very old. Needless to say, they all differed as to which radiators needed swapping, but they all arrived at between three or four radiators had to go, whilst also offering to fit the attic bedroom radiator.Small plumber advised on Worcester Bosch 30 Greenstar plus (with the control in the boiler), large local plumber said WB 30 Greenstar old (with separate digi controls), whilst British Gas recommended an 28kw boiler of their own range - apparantly manufactured by WB all the same. As for the shower, local small said shower works well with a combi, local large said shower might or might not work with a combi, British gas said you need a new shower as this one does not work.
We went with the cheapest quote, having a hunch that the shower would probably work and that his information on radiators was the most convincing one. Also, we thought, if all recommend the same boiler firm, then why not go with the cheapest quote. Ok. So far so good. Our biggest concern was the hot water flow rate of the boiler, as we often shower whilst having the washer on and maybe someone doing the dishes. Amateurs that we are, we were totally focused on the boilers abilities, hence we asked the quote to be upgraded to the Worcester Bosch 40 HE Greenstar plus, a difference of about 300 pounds - we have yet to see the final invoice. We did estimates of the mains flow rate but never measured it when all the other households use cold water as well ;-)
The whole job took almost five days to complete, two nights without heating or hot water was a bit of a hassle for a family with two young children. The plumbers first came with a WB 40 HE Greenstar convential. It took me to repeatedly point it out to them that the whole purpose of the excercise was to fit a combi and their boiler was not a combi (praise the web - makes it easy to double check), and after a brief exchange they realised the mistake - blamed it on suppliers mind you but who would not double check before unpacking that sort of equipment? The right boiler came next day and was then fitted to the outbuilding directly adjacent to the kitchen. Reason being that it's fairly large and the condensation flue needed to be somewhere where it does not blow into a neighbour's garden or window. Could not be connected that evening because the electrician was off sick.
During the installation, most of the job went smoothly. The shower works no problem (British Gas overlooked this and quoted an additional
300 pounds for the replacement shower). We did not swap any of the radiators as we thought better to check out the heating with the new boiler on, had only the radiator in the attic fitted. They used plastic pipes for the attic radiator, which had to be moved as we wanted the wall where the original tank was to be freed up in order to place some wardrobes there. We made this clear to the plumbers, but they only moved the radiator pipes. For whatever reason they left the shower pipes in place. When I pointed this out to them, they said that they did not expect the shower to be fed from pipes running through the attic. I of course in my naivity had seen this first think as the shower pipes go to the ceiling... Never mind, they agreed to move the shower pipes for another 150 quid. What do you do then? You just say ok, because you want to get the job bloody finished. Personally, I consider this borderline ripoff as we made it clear that the purpose of moving the radiator pipes was to get the corner free for the wardrobes. They are the experts to tell me that these could be shower pipes as well...But now to the biggest thing if you like concern: the end result. Heating works marvellous, a warm house with single glazing and exposed floor boards and what not. It comes on quickly and the control on the boiler are fairly sophisticated to allow for all sorts of heating scenarios. The hot water is another story though. It takes for ages to actually come through. Maybe not much longer than with the tank, especially in the kitchen, but regardless: you turn on the shower, then take off clothes and then carefully step in as it may still not be hot enough. Thank God we are not a water meter. But the real issue is the flow rate: the shower is certainly no better than it was before. Maybe about equal. And that is not so much due to the boiler but the mains flow rate in the first place. Also, I can get the shower to die instantly if I turn on the bathroom sink hotwater tap. I knew I would see less flow rate, I did not expect not to see any water at all with another tap open.
Plumber says this is partly due to the shower being piped through the attic which is probably true. But generally speaking, we have to tell people not to turn on any water either hot or cold when someone is in the shower. Now that is a major bummer I have to say. We spent the best part of three thousand pounds to *downgrade* the comfort level of our hotwater. The thing is, the boiler itself is capable enough with its 16l/35 degrees. The main culprit, imho which may be wrong, is the mains flow rate. British Gas was the only one to have concerns over this - so all credit to them for being more if you like theoretical by actually measuring flow rate. The others turn on the taps and said oh yes that will work well. The next issue is the way the house is piped is made for the tank system. You can tell that not all taps or water outlets have the same effect on the boiler. You can indeed survive the washer or washing machine coming on in the shower, but less so the bathroom or kitchen sink taps.
Another area of comfort loss is the hot water in the kitchen. The pipe is very narrow in order to give the most pressure - due to the tank system I would have thought. With a tank you then only turn on the tap a tiny bit to get enough hot water without the pressure really. But with a combi this does not work anymore as the combi basically requires us to open the tap fully in order to get the combi fire up. You can live with this sort of thing by changing your habits - always wear an apron for starters and fill the sink with hot water before washing up. But do you really want to be forced to change your habits for a new boiler? Final issue is the condensation flue. It was installed vertically, but we did not expect the amount vapour that would come out there on cold days - nor did we expect all the noise. The boiler is sound insulated except for the condensing flue which means that our vertical flue works like a loud speaker. I am sure our neighbours will hear it in their kitchen. Nobody pointed this out to us at all - we knew about condensation, but certainly not about sound.
Would we do the job again? The premise was to get the bedroom free from the tank. That much we have accomplished. By getting rid of the old system we did something for our comfort due to less worry about a breakdown, lower energy bills and for the environment by buying a A-class boiler as opposed the about z that we had installed beforehand. But hotwater comfort is crap. We are, in that sense, totally disappointed by the system. We would certainly have asked for quotes for tank systems and then encouraged the plumbers to find better places for a tank. Maybe we would still have fitted the combi, but next time round, we would be even more careful to think about the possible implications of the pipework (e.g. shower through the attic - no way!). As it stands, I can only warn people to think it through properly before fitting a combi. We find plumbers in particular to be working as empiricists, they solve problems as and when they come along, but they don't seem to be able to think the whole process through beforehand. My impression now is that we should have discussed a number of factors in more detail, the boiler specs are probably the least concern. I mean based on our experience, the Worcester Bosch website is a joke: they claim that this boiler can serve two showers at the same time - maybe in the summer with a water preheater and a second mains pipe. We cannot even open another cold water outlet in the house, so treat manufacturers claims with care. The reality probably depends more on your setup.
I hope this helps other people in their decision making. I am trashing combis, but their success depends on variables that we did not properly understand before agreeing to the job.
Fred