New Boiler Quandry

[Dustyy]

The combination of a shortly arriving baby and a 30 year old Valiant boiler over winter does not seem good so I am looking to replace the boiler with something a bit more ‘modern’

Can anyone give any advice or experience on the most reliable makes and models of boilers please? I am likely to go for a combi or condensing boiler though have heard about megaflow systems which are apparently very efficient. I live in a 1930s semi. The radiators in the two front bedrooms do not heat up hardly at all so I am going to replace all the old radiators also – should the system be flushed out before I begin replacing things?

 

[ArtfulBodger]

The megaflo is an unvented hot water cylinder and is not a boiler, but the boiler can heat the water in it (obviously!). The person who installs it must have an unvented license - make sure he or she shows it to you before he starts work - oh, and be prepared to pay a lot of money!

Your system will HAVE to be flushed by whoever installs the new boiler - the warrenty will be impaired if this doesn't happen.

I think most people would think that the more money you spend on the new boiler, the better it is likely to be - a Worcester for instance. Mid range ones are the likes of Ariston and the cheapies you can pick up from Wickes.

 

[Dustyy]

Thanks for your reply. Is a Megaflow cylinder and boiler worth the extra money for a fairly standard size semi or would a good quality combi of 100,000+ btu be sufficient?
I want to ensure that when installed whichever boiler I choose provides a power shower equivalent output for the bathroom and has sufficient capacity for possible expansion to accommodate a loft conversion en-suite and possible conservatory heating.

My current system I think utilises a primatic cylinder as there is only one tank in the loft. I know I can’t flush with chemicals but could I possibly improve the current radiator performance by draining down the system and then flushing through with just cold water for an hour or so to try and remove any sludge?

 

[blahblah]

Before you can consider the options, other than staying with a conventional system, you must determine what pressure and flow rate you have on your incoming water main. You may well find that an unvented cylinder is out of the question (unless you can accommodate an accumulator). Combis have lesser requirements but hot water supply may be an issue depending on your needs. It could be that you're better off with a new conventional boiler, sealed system, and high recovery vented cylinder.

 

[ArtfulBodger]

Really it depends on a number of variables, the main ones are:-

(1) Flow rate and pressure of incoming mains - this must be high for a combi
(2) Pattern of current and expected usage - remember that combis have inherent limitations with regard to multi-person usage
(3) Cost - the more you spend the better system you are likely to get
(4) Longevity of the equipment - it's a large investment
(5) Any other criteria, such as simplification or space saving

Generally a combi would not be a good bet for a multi bathroom house, or even a house with more than 3 adults / teenagers in it. The simple reason being that it will not be able to run two or more hot outlets satisfactorily.

A high end system boiler and an unvented HWC is both a serious amount of money and a seriously good system. But, you would have to balance the improvement against the cost to you.

There is no doubt that a top boiler will last longer as its components are of higher quality (or should be). This must be balanced against cost (again) and your perception of rapid obsolesence - i.e. do you think that there are likely to be major improvements in heating technology in the lifetime of a mid-range system.

Simplification? how about getting rid of all those motorised valves, F&E tanks, CW tanks, shower pumps, HWC's etc and reclaiming your airing cupboard. You can do this with a combi.

Personally, in a 3 bed semi with average requirements, I would opt for a decent, powerful (say 31Kw), mid range combi with an extendable parts & labour warrenty. If I could cover it for 5 years and pay less than £1K (parts) then the cost to you (excluding fitting) is circa £200 per year at worst, but possibly much less. Once it is fitted, a refit is a simple job for any heating engineer. If you do decide to go this route, then ensure that the fitters lays on an adequate gas supply to the boiler. Depending on the position of the meter and the route the gas pipe has to take, this should be at least 22mm and possibly 28mm, otherwise the boiler will be constrained by lack of gas (they burn a lot in hot water mode).

Hope this helps.

 

[Dustyy]

Thanks for your reply ArtfulBodger, good point about the gas supply, i hadn't considered that! The boiler is approx 3-4m from the gas meter and is currently supplied by 15mm copper pipe - would this be sufficient for a new floor standing combi boiler of 31kw output as suggested?
In order to provide HW back-up i was considering swapping the primatic cylinder for a normal cylinder/immersion - is this being overcautious? Space is not really a problem as the shower pipes are contained within the current cyclinder location anyway.

 

[2scoops0406]

Also important to consider the main water pipe diameter. If it's a '30s semi, the main will be likely to be a 15mm pipe. I had a megaflow in my last house, and the 15mm water main really hampered it's potential. Oh and they're dead expensive

 

[ArtfulBodger]

Thanks for your reply ArtfulBodger, good point about the gas supply, i hadn't considered that! The boiler is approx 3-4m from the gas meter and is currently supplied by 15mm copper pipe - would this be sufficient for a new floor standing combi boiler of 31kw output as suggested?
In order to provide HW back-up i was considering swapping the primatic cylinder for a normal cylinder/immersion - is this being overcautious? Space is not really a problem as the shower pipes are contained within the current cyclinder location anyway.

OK, some very simple calculations:-

A 31Kw boiler will burn about 3 cubic metres of gas an hour. If I assume you have a couple of elbows in your pipe run from the meter to the boiler, this will increase the notional length of the run to 5M. If the pipework is in 15mm copper, then that is capable of carrying just over 2 cubic metres an hour. If you increased to 22mm, then this becomes 6 or 7ish.

So, 15mm copper is too small.

Cheers

 

[Mug-o-Latte]

Only recently went for a Megaflow (or it's equivalent - an Ultrasteel pressurised 210l cylinder). We have two showers in the house, and one boiler driving them (rather than one pump per shower) We have about 9 bar mains pressure and so the showers are excellent. I don't know if a combi will provide the necessary pressure, but the Ultrasteel allows 3 bar hot water pressure througout the house, and heats the whole tank in about 20 mins as it is very efficient & fast.

If it lasts then it was the best DIY investment ever .... about £500 for the Ultrasteel and about £500 to fit, and it runs against my existing boiler. This included removing the cold water tank and having all cold water on mains too (after a sh*t the bog fills up very quickly !)

Don't know how this compares against the cost of fitting a combi.
MOL.

 

[ChrisR]

Mains much above 3 bar is not all that common. I was recently asked to fit a Megaflo for £2000. The mains pressure was about 2.5 bar, on a 15mm pipe giving total cold water flow well under 20 litres per minute. They had been using a 4 bar pump on their shower, which would of course have to go.
I refused.