The age old boiler question!

I'd like a bit of advice please.

My elderly parents presently have an old Glow Worm 65/80 floor standing boiler in the basement, it runs 20 radiators (that's counting doubles as 2) and the hot water tank.
The property is a chalet bungalow, their bedroom is on the ground floor, they recently converted the huge loft space and installed 5 more rooms up there (god knows why!!!) 2 of those rooms are heated but in the other three, the hot water for the radiators doesn't make it that far, the supply pipes for those has to go up and over what's left of the loft space, run alongside the CH supply tank thus resulting in "negative head"....... not the main question here... but would a pump solve that problem?

The flue from the boiler is plumbed up through the old chimney along what appears to be an 8inch asbestos pipe, it feeds the main circuit on 22mm pipes and the gunfoss 3 speed pump hums happily away next to it.

My parents want a more efficient boiler (we're told a pressurised system would solve the negative head problem for the 2 loft radiators)

What I'm wondering is if a condensing combi would be the way to go, if so, would the flue still be ok to go up the chimney, I'm thinking the flue output will have lots of water vapour and not sure if it'll just condense in the brick stack and saturate everything. There is room for re-siting the boiler and flue outlet to an outside wall.

Would a floor standing conventional boiler be the easiest way to go, if so, how would the negative head problem be solved, the cold water storage tank won't raise any higher.

Then we get into the pressurised hot water systems, another friend has one of those beasts fitted and that ones way beyond my knowledge, I'm already skimming the bounderies with everything else above!

I'd be gratefull of any feedback

Pye said:

My parents want a more efficient boiler

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All boilers are rated according to efficiency, look for an 'A' rating

Pye said:

We're told a pressurised system would solve the negative head problem for the 2 loft radiators

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Correct. A system boiler is pressurised from the cold mains supply and has an internal pressure vessel to allow for expansion, no header tank required.

Pye said:

would the flue still be ok to go up the chimney

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New boilers have a balanced flue. This has 2 sections one where air is drawn in and another where steam and fumes are expelled. The boiler is sealed from the room. However, the boiler you have now draws in its air from the room (that you've paid to heat) hence the need for an airvent in the room to allow it to be replaced, and the fumes go up the chimney.

Pye said:

What I'm wondering is if a condensing combi would be the way to go.

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Condensing yes, (they all are condensing now anyway)

Regarding the combi part, I would consider having a condensing heat only boiler unless you are desperate to gain the space occupied by the hot water cylinder. Heat only boilers are still condensing so keep all of the efficiency benefits, and a system version will overcome the 'head' issue.

Combis are great for some complete new installs as they avoid the need for the hot water cylinder, but not always the best solution for existing installations. Here's why you might want to have a heat only boiler.

1. You won't have to get rid of your existing hot water cylinder and pipework, which will be less disruptive. You also retain the airing cupboard facility and the back up of an immersion heater.

2. Combi’s are more complicated than heat only boilers so they have more components inside, thus increasing the possibility of a failure. (A search on this forum will highlight the problems with diverter valves responsible for the change over from hot water to heating.) As they are heating mains water, if you live in a hard water area they can be prone to a build up of limescale (furring) which shortens their life.

3. Combi’s are slow to get hot water to the taps if the boiler is starting from cold. The boiler has to heat up its own internal heat exchanger then transfer the hot water to a secondary heat exchanger before heating the water going to the taps, not good if you're on a water meter, or waiting to wash your hands. You could of course use the preheat setting that fires the boiler every so often to keep it warm just in case you need some hot water (Personally I see that as wasteful, like starting up your car every half hour to keep it warm, should you want to go out)

4. To generate hot water directly from the cold mains supply, Combi boilers have a larger gas burner. Because of this, you will most likely have to have a larger diameter gas pipe to the boiler to cope with the higher demand. Often in boiler upgrades, this unsightly pipe is routed around the outside of the house.

5. Combi boilers cannot provide hot water and heating at the same time. When supplying hot water the heating will go off.

6. Combi’s heat cold mains water that passes through the boiler to supply the hot taps. The supply has to be shared with the cold taps, WC’s, washing machines, dishwashers, etc., If any of these are used at the same time as the hot water, the hot water supply will be reduced accordingly.

Pye said:

Would a floor standing conventional boiler be the easiest way to go

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You can't fit a conventional boiler now, it has to be condensing.

The answer to this one is much simpler than all of the above. Ask lots of people you know to recommend a good installer, and let him do what he thinks best.

The reply from Stem, though no doubt given with all good intentions, is incorrect as well as incomplete, which is not surprising as he is not a RGI.
One thing is for sure, it would be a lot better if the new boiler went in a different location, the rest depends on the particular situation.

You will probably get a lot more replies from all sorts of people and as a result you may end up being more unsure than you are now. You may want to ease that by checking each poster's profile and if it does not say registered gas installer or heating engineer, you should just ignore it. Let's face it, you wouldn't ask a builder how to fix your car or a car mechanic how to build an extension.

bengasman said:

The reply from Stem, though no doubt given with all good intentions, is incorrect as well as incomplete, which is not surprising as he is not a RGI.

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You don't need to be an RGI to know that Combi's can be slow to heat hot water starting from cold, they share the cold main supply with everything else, and can't heat rads and hot water at the same time? Most users will confirm this. It's no different to a car driver telling you about the features of his car. he doesn't have to be a mechanic to do that.

You are quite right of course, I an not an RGI and the heating systems I work on are of an industrial nature. Steam, heat exchangers, heated ringmains etc., but the principles are the same. Over the years, I have also met some qualified heating / gas engineers who might know all about flues, can repair appliances quickly and safely, know how to test etc., but were ignorant of some very basic principles of operation. My guess would be that you probably know some too, or al least you've come across their work.

Thanks for that Stem, answered lots of stuff to what I thought was a minefield of questions.

I'm figuring keeping the hot water tank in the loft (space isn't needed) and having the boiler replaced as is for a modern one.

my only two concerns are the exhaust, I'm assuming the balanced flue prevents it venting into the chimney stack, the boiler is in centre of the huge cellar, which is always toasty and warm due to the inefficiency of the boiler, so I'll either need to have the boiler resited or have a 4 metre horizontal flue..... which seems a tad excessive!

would the new system be pressurised? I thought it'd be another open vented system and need a header tank, if not, would the open piping be capped off and how would the hot water system feel about being pressurized?

Thanks for your input on all this, it's much appreciated.

bengasman said:

The answer to this one is much simpler than all of the above. Ask lots of people you know to recommend a good installer, and let him do what he thinks best.

Let's face it, you wouldn't ask a builder how to fix your car or a car mechanic how to build an extension.

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I appreciate your comments bengasman, but I like to understand what work I'm having done and the reasons why it's being done, I understand every trade has good and bad, but I'm aware of a few situations were qualified tradesmen do work that's not always necessary, a prime example being new heat exchangers being fitted when the old one could easily have been cleaned out and replaced, another situation where a pressure vessel was fitted because the fitter "thought" it would solve the boilers constant loss of pressure (turned out to be a perforated heat exchanger... not before he charged £300 for fitting the pressure vessel)

I think an understanding of how things work is always useful, especially if there's a problem at stupid o'clock in the morning and the tradesmen at the other end of the phone is firing questions as he/she tries to determine what the remedy would be.

You make your own choice with the combi versus system boiler question. Most people are happy with combis now, and most of the supposed disadvantages are not that great, and there are positives as well.

boilers can have a flexible liner up an existing chimney stack, used as either a conventional flue, or as a vertical balanced flue. This keeps the condensate plume up and away.