New Gas Boiler

[Paulgertie]

 The majority of boilers are much of a muchness and different plumbers will have their favourites. I know some plumbers swear by boilers I wouldn't touch. Saying that I'd make sure it has a stainless heat exchanger whatever make it is, the condensate is corrosive and it's reckoned they last longer.
 Combi boilers are not necessarily the best boilers for all, plumbers love them because they are quick and easy to fit. They give mains pressure hot water, good for showers, but at reduced flow due to passing through boiler slow enough to be heated.. This causes problems if you have more than one tap on at a time, even a washing machine with cold fill only will cause pressure to go up and down. Flats or households with only two or three people in them they may be OK for, but more than that, especially if you have a second bathroom, I wouldn't recommend them. One big advantage is you only heat the water you use. From a family point of view if you have a cylinder with the immersion you have a backup should the boiler fail.
 As luck would have it I went to a presentation last week about air source heat pumps see http://www.trianco.co.uk/activair.cfm. I have to say myself and most of the plumbers there were greatly impressed, from a cost, performance and installation point of view they are great. Much cheaper than solar, works rain or shine and is compact. Had a demo of the unit going and while we were there it heated about five gallons of water to over 40c in maybe two hours, not bad from cold. You can download a pdf of the brochure from the site. Yes they are trying to sell the product, but some stuff sells itself, worth a look.
Paul

[Paulgertie]

Rog, one of my plans is to replace our boiler with a combi which can take pre-heated water. The idea is to have solar collectors (on the garage) pre-heat the water in a tank before passing into the boiler which would 'top up' the temperature. From memory you need a water tank which can withstand mains pressure and so they are not cheap. Doesnt answer your question but might be worth considering when choosing a boiler.

Steve, a reasonably simple way to do this would be to use a cylinder in reverse, use the solar to heat the cylinder and run the mains water through the coil, the coil should be rated to at least 3 bar on a normal cylinder as this is what sealed heating systems are rated to. I you get a high recovery cylinder the heat transfer should be pretty good, not as efficient as using a mains cylinder but significantly cheaper. All combis will take a pre-heated source mains fed and depending on design pump fed.
Paul

[johnr]

paul, whilst all combi's work in pretty much the same way, I have to say that I don't find them all the same. there are some which stand above the rest in terms of build quality and reliability. i'm not going to list them here, but combi's like bikes, aren't all equal, though they all do roughly the same thing. also its worth mentioning that NOT all combi's will take a pre heated cold feed. the solution for those that wont is to use a thermostatic mixer valve on the hot feed AFTER the combi.

air source heat pumps, like ground source ones are touted as the future technology to watch, but im not convinced, they still require a reasonably large quantity of electricity to run them, despite their obvious efficiency advantages over gas heating, and the heat pump technology is pretty specialised stuff to maintain, you think plumbers are expensive, try calling an a/c guy out, that will really make you wince! i think its too young a technology to throw money at just yet. its getting there, but its still not quite up to the mark. i went to the worcester technology centre last year, and they were just running load tests on their greenskies ashp unit, and whilst it looked promising, its still not quite powerful enough.
finally, theres the water byelaws to take into account. if youre planning to run a cylinder in reverse like you say, then you will still need to be aware of the regulations governing unvented hot water systems, which is in fact what you will be making, and the possible legal pitfalls of such an installation. im not saying don't do it, but im just pointing out that the supply of water is quite strictly governed in the uk for a reason, and if you choose to break the rules, at least be aware of what they are. 'it was only in my own house so affects no one else' isnt an excuse that would stand up in court.

[Steve H]

Ive found this thread quite interesting

also its worth mentioning that NOT all combi's will take a pre heated cold feed. the solution for those that wont is to use a thermostatic mixer valve on the hot feed AFTER the combi.

Is there anyway of telling the difference ?

finally, theres the water byelaws to take into account. if youre planning to run a cylinder in reverse like you say, then you will still need to be aware of the regulations governing unvented hot water systems, which is in fact what you will be making, and the possible legal pitfalls of such an installation. 

Do the correct cylinders have some form of pressure relief to ensure the pre-heated water does not overheat and presurise the mains supply ?

[Paulgertie]

 I've mailed Johnr about the combis, because I'm unaware as to a reason why some combis would not take preheated water.
With regards to cylinder you can fit a twin coil cylinder, with the cylinder being open vent. If you look at the product sales brochure 12kw system diagram you could just swap the underfloor heating section for the mains supply to the combi. With a SolarTwin panel system you could just use a single coil cylinder because the water is heated in a vented cylinder and you would use the coil to run the mains water as previous. I'm looking at this method for my parents place in France. All the previous methods would get round the unvented hot water regulations, which apply to stored hot water under pressure pointed out by Johnr.
Paul

[Paulgertie]

 Seems some manufacturers do advise against preheating water, so the only thing is is to sort out a couple of boilers and talk to the manufacturers.
 One major thing Johnr did point out to me is there are lots of places with higher than 3bar mains pressure which would stress a standard cylinder, therefore you'd need to pressure test your mains and use a pressure reducing valve to bring it down to around 2 1/2bar. It's worth mentioning you need a minimum of 1/2bar, though I'd recommend at least 1 bar.
 I personally do not think a non-return valve is needed as the temperatures using a cylinder as described would not cause that much expansion. The unvented cylinder have temperature and pressure relief and these cylinders can only be fitted by a suitably qualified person.
 One thing to remember is that with HIPS around now if you want to sell your house it will need a report which shows energy efficiency and correct installation.
Paul

[guest27]

We should be OK as to pressure as we had the connection to the mains checked not long back - making sure there was no lead pipe in there,- the water board man went a little pale when he saw where our water was coming from.  As far as he could tell it was connected (via a reducing valve) to the 14" main that serves our village and half of Port Talbot. The tap was leaking - which is their tap - he just said we would wait until it failed...

Mind the rusted steel pipes would probably fail if the pressure was too high.

What this has to do with thumpers I do not know.

R

[Paulgertie]

What this has to do with thumpers I do not know.

R

Nothing, which is one of the reasons I like it here, someone goes off on a tangent and people just go with it, bit like chinese whispers.
Paul

[themoudie]

If you heard my neighbours ball valve hammering every time they draw water, you'd know what this thread has to do with thumpers!  

Our water supply used to be a cast iron 2" pipe supplying water to cattle troughs and 5 households. When tested we had over 2000ppm of Fe and if the cattle drank water the washing machine wouldn't fill! We renewed the main ourselves and the pipe was that full of silt and corrosion that you could only make out the diameter of a straw in a 6" length and maybe see daylight.   Needless to say 18 months after replacing the pipe, Scottish Water came and connected us to Perth town water which is abstracted from the Tay 5 miles away and pressure is way over 3 bar.

This thread has been good, because I have been 'contemplating' various alternatives to mains gas 22 years old cast iron boiler for 2 years now. However, plumbers have advised us to stick with what we have (Ideal Mexico) until it blows up, as you have to recoup the cost of the new set up.

Probably go for an open vented mains gas condensing boiler, into a twin coil stainless mains pressure Maxi cylinder with either solar or wood boiler input into the other coil. You get hot water at mains pressure, which is useful in a wee house like ours, with poor header tank height. Can't get my head round how to do the central heating bit as well, need diagrams

Need more insulation in the loft afore going down this route, only about 6" at best up there and would it be better to get the 40 year old wiring renewed afore laying fresh insulation, and treating the woodworm, as its 25 years since that was done? All suggestions, comments welcome!!!

Alternatively, go out and ride the bikes, as a motorcyclist "Never knows!"

Boppin', Bill

[Paulgertie]

http://www.google.co.uk/imgres?imgurl=http://www.causewayheating.co.uk/images/whichboiler3.gif&imgrefurl=http://www.causewayheating.co.uk/whichboiler.cfm&h=324&w=302&sz=14&tbnid=saNPriqkvv4J::&tbnh=118&tbnw=110&prev=/images%3Fq%3Dopen%2Bvented%2Bcentral%2Bheating%2Bdiagram&hl=en&sa=X&oi=image_result&resnum=3&ct=image&cd=1

Bill, above gives you diagrams for 4 different systems, obviously you will have an extra coil on the cylinder. I'm curious, especially given your poor header tank height why you are opting for open vent.  On the boiler heating and hot water coil a sealed system would be more efficient and with faster warm up times. There's no reason not to have the wood or solar coil vented if you wanted, dependant on the system you put in. You would then have a traditional heating system on one side and just the extra coil to provide alternative heat. You're only other problem would be which controls to use to decide on which heat source you're using for the cylinder and to control temperature and times for each.
 
 You will need to do wiring and woodworm treatment first and put in as much insulation as you can get/afford. I think in Scandinavian countries they have 18" and more, granted they are colder there, but everything you lose you pay for.
 
 With regards to water hammer, besides the ballvalve it could be the stopcock hammering and can sometimes be relieved by slightly opening or closing the valve, I replaced mine to solve the problem. Funny enough even my neighbour using the mains water would cause it to hammer, as we have a shared mains.

Paul

[themoudie]

Good evening Paul,

Thank you for the URL and info, much appreciated. More pondering!

My regards, Bill.

[johnr]

just an update on this ancient thread. ive just bought myself a new solar panel and water cylinder alongside a new combi boiler, and am in the process of fitting it into my new house near blackpool. when its done, anyone who wants to see how it all works is welcome to come and look, or ask what they like.