Megaflo and system boiler - Who is right ?

[cam123]

Could any heating engineers offer me advice on the following please? So far I have had two advise and they totally contradicted one another!

Situation: I have a property currently laid out as two separate flats, each has a combi boiler. The property is gradually being turned back into one 5 bed 3 bath house - ultimately with a megaflo or other unvented cylinder and a system boiler.

It is a bit of a non-standard situation because we are living in one or other of the flats throughtout, and the renovation is happening in stages, with the new system boiler going in the brand new kitchen extension, which is not scheduled until next year. Until then, I need to keep things running off the combis.

The cylinder however is to be situated on the first floor, in the upper flat, which is being fully renovated now. I am trying to ensure that everything that needs to be done for a smooth transition to a system and cylinder is done now.

Engineer 1 says: Put in your megaflo now, attach it into your upstairs combi as a temporary measure, until the system boiler is put in next year when it can then be transfered over. This will allow us to test the new pipe runs with the cylinder. Also, you need to ensure there is a secondary return on your hot water put into the bathrooms now, going back to the cylinder.

Engineer 2 says: Don't bother with a megaflo now as it can't actually be connected into the combi for temporary use. Wait, and do the combi at the same time as putting in the system boiler. In terms of pipe runs, nothing extra is needed on the top two floors for it all to work with a system boiler and megaflo - no secondary hot return needed.

I realise that the timing of the installation of the megaflo is quite a subjective issue, so i'm not too worried about that (i'd be tempted to wait so as not to incur costs of doing some change overs twice) but i am baffled by the secondary return issue - which I need to sort out now whilst my fix fix in the top flat is happening.

Thank you to all offering their thoughts and i hope that the above is clear enough to give a decent idea as to what's going on!

 

[simond]

Without seeing the job, both suggestions could be valid.

 

[ALEC1]

you certainly need to get pipes in before you get too far a head...


with out seeing it no one can say for sure what is necessary...

 

[JohnD]

(he says) "Don't bother with a megaflo now as it can't actually be connected into the combi for temporary use."

Oh yes it can! it is a perfectly straighforward job and any heating engineer or plumber should know how to do it.

The only exception I can think of is a very young or inexperienced one who has not been trained, and only knows how to fit combi boilers (they most often are not installed with cylinders) as a quick and cheap job.

 

[ALEC1]

it also depends on the final boiler... no point in investing in diverters and two ports if the boiler at the end of the project has its own diverter and cylinder sensor...

 

[cam123]

Ok, so can anyone explain to me under what circs I would need a secondary return and under which circs I wouldn't? Then from that I can work out which I fall into. This is the realy critical issue that i need to deal with and put it in or not next week.

The 2nd engineer actually then qualified what he said with "well you can connect your combi to a megaflo cylinder but really it'll only be being used as a big radiator".

 

[ALEC1]

secondary returns are used with long runs to the hot water taps from the cylinder to reduce wait times at the taps...

correctly installed they can save water and energy but they need to be properly controlled to reflect demand, not left running..

with decent boilers you can control them on the main programmer for the heating and the hot water...

 

[cam123]

Right ok, that makes sense. So without a return i will have to wait for the hot water to feed through from the cylinder?

I have purposefully chosen a location for the cylinder in the middle of the middle floor of the property, so the furthest away shower would be around 3m of 22mm and 4m of 15mm pipe away - is this considered a long enough run to justify a secondary return? All other outlets will be less than this.

 

[ALEC1]

No... its a nice thing to have but not strictly necessary at those distances..

thats unusual to think about plumbing and heating...and reassuring that such clients exist...!!

 

[Boilerman2]

Whilst I haven't seen the property in theory I favour Plan No.1 get the HW cyl in now fed by the existing Combi, (my judgement is based on years of Hotel refurbs )

 

[Dan Robinson]

+1 for option 1. the engineer that said it wasn't possible should be dropped - quickly. he obviously needs to go back to plumbing school.

 

[cam123]

On the secondary return point i see that it really could be either way, and basically it comes down to if I want to pay the price (new pipe run, pump, installation, timer, running costs) of the super-convenience of having the hot water come out of the tap straight away as opposed to after a couple of seconds. Hmmmmn...

As to installing the megaflo straight away with the temporary combi, what are the advantages of this? So far i can see that it has the advantage of being able to test my new pipework with the cylinder in situ, but it does have the disadvantage of then having to double up on connection costs when it is taken off the combi and put onto the system boiler. Is that it or am i missing finer points here that matter?

Thank you everyone, this helps alot.

 

[JohnD]

IF you have a very good incoming water flow (some say 20 litres/minute) then a Megaflow will give you fantastic delivery of hot water, and you will not be troubled if someone else turns on another tap while you are in the shower (this is a big problem with Combis). Depending on size, the boiler will take about 20 minutes to heat up enough for a bath, but you can fill the bath perhaps twice as fast as the combi can manage..

If the incoming water main is a weedy half-inch lead one, you can probably get a subsidy to replace it. If you're going to the trouble of laying a new one, I'd go for 25mm or even 32mm right up to the pavement.

 

[ALEC1]

the OP is in London and there are no subsidies for up grading from lead... costs from £500- £1500 but a better option than a home boost...

 

[JohnD]

the OP is in London and there are no subsidies for up grading from lead

There was last time I did it in London, provided they test your drinking water before you start work, and it contains sufficient traces of dissolved lead. They will also replace their lead pipe connecting to yours if any (there usually is) which is easier than doing the connection yourself, or having to pay for it
http://www.thameswater.co.uk/cps/rde/xchg/corp/hs.xsl/11025.htm

Ask them to test ther lead content quickly, as they are quite slow to do it.

In my case the old pipe was actually leaking, so I got the "replace a leaking pipe" subsidy, which was then "a subsidy of £ 215 to fully replace the supply pipe between the edge of the public highway and the inside stop valve"

That was in 2010.