Payback time on new boilers

[Set Square]

Based on discussions in other recent threads, it seems to me that there can seldom be a financial justification for replacing an operational boiler purely to achieve higher efficiencies and lower running costs.

Looking at my own situation (12-year-old Baxi Solo 70/PF) - using the information on the Sedbuk site

then "View Efficiency Database" and scroll down to running cost table] the best I could hope to achieve by going from an old light-weight boiler to a modern condensing boiler would be 25% p.a.

Since I currently spend about £400 p.a. on gas, I might hope to save £100 p.a. Assuming a £2k project cost for sourcing and installing a new high-efficiency boiler, it would take about 20 years to break even, by which time I'll be over 80, and the 'new' boiler will be long-since dead, even if I'm not!

Of course, one would normally upgrade the control system at the same time - increasing overall efficiency a bit more in the process. In my case, I have a fully interlocked boiler (Y-Plan) already, so my boiler isn't needlessly keeping itself hot. However, I don't have TRVs, and am conscious of the fact that some rooms are too hot some of the time in order to ensure that others are hot enough.

I suspect that's it's much easier to justify the outlay on tweeking the controls - particularly if you DIY. I reckon I could probably save £50 p.a. for an outlay of about £200 if I were to fit TRVs on most rads whilst keeping the current boiler - and this is a much more pleasing proposition.

Looks like my project for the summer is mapped out!

[Mike]

Totally agree with what you say. But not convinced TRVs always save money as they will still heat rooms when not likely to be in use.

We discussed making controlled valves using a TRV body and a simple programmable timer some time ago and the payback on this can be only a couple of years, depending on your circumstances of course.

[John Stumbles]

Not to mention that you'd have done better putting the money in a savings account and earning intereste on it (or not borrowing money for the project and paying interst on the loan).

Even where you have to replace a boiler anyway, at current price differences you'd be hard pushed to make money on replacing it by a condensing rather than non-condensing boiler.

Probably for most people the best return on investment is draught proofing and insulation.

[Christian McArdle]

Absolutely. The environmental benefit is often to maintain the older less efficient boiler. The new boiler has environmental cost in its production and transportation.

Absolutely again. If you are DIYing, I'd be surprised if you'd spend 200 quid on TRVs. Say 15 quid a rad for a good quality mid-range valve, you'd need to have a big house!

Christian.

[Christian McArdle]

Yes, but at least they'll only be heated to 21C, rather than 30C. That could (in fact will) make a huge difference.

I never got around to doing this myself, unfortunately. However, I've got most of the benefit by subzoning in bedrooms/downstairs receptions/kitchen/conservatory/loft conversion. The last two aren't implemented yet, although the pipework is there for them.

Christian.

[Rob]

Interesting post, just what I wanted to hear! I still haven't got round to replacing my Glow worm Space Saver 60B MkII. When I asked around, most recommended a condensing combi, some a non-condensing combi and some just leaving it alone. Because of the confusion and expense, and likelihood of leaks on going to a pressurized system, I'd defaulted to leaving it alone for the moment. It's simple and reliable, which counts for a lot, especially having read so many tales of modern boiler problems on this group. I would, however, like to know what financially justifiable improvements, DIY especially, I could make to my simple system, particularly the gravity hot water side. There are no motorized valves or cylinder stat. All eight radiators have TRVs, except the bathroom which is permanently on. The system has a Grundfos UPS 15-50x18 pump for the heating, Potterton EP3000 controller, and a Landis & Gyr thermostat in the hall of the bungalow. I'm considering a DIY powerflush sometime because however many times I flush it manually, it always returns to running on black water within days. Any other recommendations? (Other than the expected advice to get a combi, or two...!)

Rob

[Set Square]

I suppose that the ultimate in efficiency is to have an S-Plan+ with a separate zone in each room, to which the above suggestion would get somewhere near.

However, in practice, I'm not totally convinced! It would be expensive to implement because you'd need a programmable stat (at 40+ quid a throw - more if wireless) in each room and a lot of wiring. Also, I'm not sure whether TRV body variety of zone valve has the necessary volt-free contacts required for boiler control. Above all, unless you have static temperature vs time profiles for each room, it would be a nightmare (for anyone other than nerds like us, anyway!) constantly having to re-programme the programmable stats.

I think I'd go with the TRV approach. OK, that doesn't give different heating profiles for different rooms - but it's quite easy to nip round and give a TRV a tweek if needed.

[John Rumm]

If it ain't broke, then don't fix it! When it does need replacement then you may as well replace with the most reliable and efficient boiler you can find.

I was anticipating that problem myself... in the end however it was all a bit of a non event. It pressurised, and off it went.

The obvious change would be to go to fully pumped hot water, that would give you faster recovery and the ability to _not_ heat the water when you don't want to.

Going fully pumped would add a cylinder stat and a three port valve as a minimum. Possibly a new controller if your current one does not support independent control of HW.

The other "quick fix" that can make a big difference is changing to a programmable thermostat. This will let you specify different temperatures for different times of the day and night. Hence you can set it to drive the system in a way that is appropriate for your usage without needing to manually tweak the stat all the time.

If you are adding inhibitor after refilling, and the radiators are getting uniformly hot (i.e. no cold sections due to piles of sludge!) then probably not much to worry about.

[Set Square]

If your boiler works and doesn't let you down or cost a fortune in maintenance, keep it!

One thing which would be well worth doing is to convert it to a C-Plan system for which you would need a zone valve and cylinder stat. Not only would this control the hot water at the desired temperature - rather than having it drift up towards boiler temp - but it would also provide a boiler interlock - turning the boiler off when both HW and CH demands are satisfied rather than wasting fuel needlessly keeping itself hot. You can see briefly what this entails by looking at the first part of

only things you have to watch are that you install the zone valve in the gravity HW circuit in a place where it won't interfere with a clear path fom the boiler to the F&E tank, and that the zone valve itself has change-over type volt-free contacts which change when the valve is fully open.

You could also consider a programmable room stat in place of the existing one. This would enable you to vary the overall heating level at different times of day and would also allow you to have the hot water and heating on at different times from each other if you wished.

If your hot water currently takes too long to heat up, you could convert to a fully pumped Y-Plan or S-Plan system, but this would involve more pipework mods. If the HW performance is adequate, I wouldn't bother - particularly if your HW requirements are predictable and if you decouple the timing of HW and CH as discussed above.

As far as flushing goes, you didn't mention inhibitor. Have you got some in your system? If not, flush it out and put some in! This should stop the water getting black quite so quickly. I wouldn't bother with a power flush (expensive!) unless there's evidence of blockages or cold centre-bottom sections of radiators.

[Christian McArdle]

Actually, there are advantages of the proposed system over s-plan-plus. This is because the TRV bodies lent themselves to analogue modulation of the flow rate, although the proposed solution included microprocessor control of the entire system, rather than a simple timer.

The conclusion I came to was that the maximum benefit in terms of cost vs efficiency was to divide off bedrooms, kitchens and conservatories, which could benefit from very different temperature profiles to reception rooms. However, the advantages between individual reception rooms and between individual bedrooms were too slight to justify the additional valves and repiping, IMO.

Christian.

[Christian McArdle]

Particularly as any leaks at this point were a sign of impending doom anyway. If a pipework system can't handle 2 bar, then it is pretty shot already.

Christian.

[Set Square]

Nice if you can do it. However, it wouldn't work for our house for 2 reasons.

Firstly, the main CH flow and return pipes run between the floors - with connection points for upstairs and downstairs rads being randomly distributed - so it's not possible to separate into Up and Down zones.

Secondly my wife and I each use an upstairs room as an office - and spend quite a lot of time upstairs in the daytime. [We are both retired, and have many interests which involve using computers to some extent]. So we would need 2 upstairs rooms to be differently controlled from the others.

[Christian McArdle]

Yes, I was lucky to find that I had a 15mm upstairs trunk separate from the

15mm downstairs trunk and joined just above the understairs cupboard to a 22mm joint section. Easy to split here and install the zone valves in the understairs cupboard.

Obviously, people's usage patterns do vary!

Christian.

[Rob]

Thanks for the suggestions.

Hot water quantity is fine, so probably don't need fully pumped. (Only problem is the flow slows to 4 l/min. shortly after turning the tap on. I think it's caused by insufficient head, but that's a separate issue). The Potterton controller manual has diagrams for gravity HW, with or without cyl. stat., HW control valves: spring return with DT switch, or motor open/motor close. Also fully pumped systems, so it sounds like it will do what I want, if I can figure out what it all means. Possibly beyond me as a DIY job. Programmable room stat. sounds good.

System has always had inhibitor, Fernox initially, Wickes for a short time, then Sentinel after a Sentinel flush. No radiator cold spots but the water in the expansion tank is black as night. The guy who installed my gas fire recently had a look and said it wouldn't bother him. Mind you, he had an interestingly casual approach to installing gas fires, so possibly not to be believed.

Rob

[Ed Sirett]

I agree the control system is about as significant as the boiler itself.

An old style boiler with electronic ignition and a fan assisted flue (say a Pott. Profile or Neatheat) together with state of the art external controls would probably out perform a condensing unit on a simple time switch with no control of the HW.

[IMM]

proposition.

Are you having a laugh?

[Roger]

The message from Ed Sirett contains these words:

Careful Ed. You have moved into dIMMS 'snip drivel' territory by praising the virtues of a boiler with a cast iron heat exchanger. :-)

[IMM]

< snip drivel >

[Set Square]

Note that if you go for a D-Plan, you must 'lie' to your programmer, and tell it that you haven't got a gravity system, even though you have! This is because on the gravity setting it automatically forces HW on whenever you select CH - which isn't what you want, because you now have *independent* control over HW and CH. This is especially important if you go for a programmable room stat and opt to have HW and CH on at different times. [You would achieve this by setting HW to timed and CH to Constant on the main programmer. The HW would come on whenever the main programmer was on, and CH would come on whenever the programmable stat told it to - which could be at completely different times].

[Set Square]

For D-Plan, read "C-Plan" - that's inflation for you!