Advice on new (combi) boiler and/or Megaflo

[KingsGambit]

Hi all, I have just signed up after almost every web search I've made has brought me to one of the many posts in this very forum. I've learned a lot from reading it all but hoped to presume for a little advice on my specific situation from some of the very helpful people here. I have a small handful of questions, related and not and my gratitude in advance for your advice.

I've just bought my first home, a 3-bed semi in NW. London. At present it has a (traditional) boiler (in the very small kitchen) with a hot water cylinder in the sole bathroom and storage tanks in the loft. I very much would like to get rid of the lot and get a new combi installed in the loft (once it's boarded and old system removed).

After so much research on the web I've come to understand that showers with a combi can be tricky and seem to be almost wholly dependant on mains water pressure which I gather can vary and understand by law cannot be pumped. I know neither what my mains water pressure is, nor how to test it.

In order of preference my priorities are:
Consistently good shower pressure
Hot water on demand
Long-term savings on energy bills
Upfront costs

I've just learned about the Megaflo system and further from this site, the Alpha Flowsmart system. What I don't understand is how these various systems interact and the negatives to each. Would a top of the range combi (Worcester Bosch, Vaillant presumably?) with a megaflo suit my needs? How might they be fitted to best utilise them? What about the Vaillant 937 boiler that has some sort of storage system? I'm of the mindset that perhaps if I have a system that can cope with every water outlet being on simultaneously then I would never need to worry. Is there a downside to overspeccing beyond the upfront costs?

Further, I'm considering having a wet underfloor heating system installed throughout the ground floor (approx. 30-35 m2). Would this affect my choice of boiler?

Lastly, and unrelated to the above, I'm hoping to install a W/C under the stairs (pending what looks like some complicated electrical relocations). It's made complicated by the hall being on the shared wall, not the outer wall and while I don't mind the floor being dug up to run new pipes, I've been advised that there may not be enough of a gradient for the pipe to drop, so might consider a Saniflow system. What is the downside of having a saniflow installed? There is approx. 4 meters from the location to the nearest available drainage and a drop of about 300-350mm without digging anything up. Is that enough for normal pipes?

My apologies for the bulk of text above, I'm a very fast typer. Any advice from the knowledgable professionals or experienced homeowners would be very gratefully received.

 

[mysteryman]

Either of these systems has to be fed from the cold water main, which will need checking.

You have defined the basics of a good combi system - this you will find very satisfactory as long as your expectations are reasonable. There are many, many millions in use with satisfied users. There are also people who will knock them. It is your choice.

I would do almost anything to avoid using a macerator for a bog. The soil pipe requires a 1 in 40 fall.

 

[bengasman]

I've come to understand that showers with a combi can be tricky and seem to be almost wholly dependant on mains water pressure which I gather can vary.

Not really tricky, your mains will allow it or not.

If you are into research, find out the following; you will need to understand it if you want to understand what make a combi work properly.

The difference between flow and pressure.
The difference between static pressure and dynamic or working pressure

In order of preference my priorities are:
Consistently good shower pressure

See above.

Long-term savings on energy bills

Draught proof, insulate, and heat the house up less long and less hot.

Upfront costs
I've just learned about the Megaflo system

For get about the Megaflo is cost is an issue; they are more expensive to run and more expensive to install.

I'm of the mindset that perhaps if I have a system that can cope with every water outlet being on simultaneously then I would never need to worry. Is there a downside to overspeccing beyond the upfront costs?

Creating a system that will alwasy peform well regardless of demand will be a very expensive exercise; apart from expensive kit it will also require re-plumbing back to the streetvalve.

Following the old adage that you can not have your cake and eat it, you need to sit down and make up your mind about what has priority: budget or performance; the two are mutually exclusive.

 

[KingsGambit]

You have defined the basics of a good combi system - this you will find very satisfactory as long as your expectations are reasonable. There are many, many millions in use with satisfied users. There are also people who will knock them. It is your choice.

I would do almost anything to avoid using a macerator for a bog. The soil pipe requires a 1 in 40 fall.

Is the idea of combining a combi boiler and megaflo worth considering then? And why would you prefer to avoid the macerator whereever possible? While the location in the property is an ideal space, it's not ideal for plumbing and with the 1 in 40 drop you mentioned, it may be a little short (40cm for the 4m distance, where perhaps only a foot or just over is available). The benefit of being able to run a small pipe without worry may outweigh the negatives perhaps?

I've come to understand that showers with a combi can be tricky and seem to be almost wholly dependant on mains water pressure which I gather can vary.

Not really tricky, your mains will allow it or not.

That's what I meant, my apologies. It's the hit or miss factor, combined with there being very little that can be done to alter it that I meant was tricky.

Upfront costs
I've just learned about the Megaflo system

For get about the Megaflo is cost is an issue; they are more expensive to run and more expensive to install.[/quote]This is likely to be an expensive endeavour anyway with relocating and replacing much of the system. I don't really mind spending a little more once-off for the long term benefits. But would the above suggestions prove a good system for the house?

Many thanks to you both for the great tips already.

 

[Hugh Jaleak]

Macerator's can prove somewhat troublesome. The golden rule is dont put anything through the macerator that hasn't been through you! Anyone who isn't aware of the limitations of it can soon cause problems. Unblocking and cleaning a Macerator is not a job for the faint hearted!

You need 100mm of fall over 4 metres on a soil pipe, if there's a foot available that would be ample. I'd go for a 110mm pipe anyday over a macerator. 110mm pipe is more fit and forget, done properly the chances of it blocking are a lot less than chances of Macerator problems.....

 

[KingsGambit]

Macerator's can prove somewhat troublesome. The golden rule is dont put anything through the macerator that hasn't been through you! Anyone who isn't aware of the limitations of it can soon cause problems. Unblocking and cleaning a Macerator is not a job for the faint hearted!

You need 100mm of fall over 4 metres on a soil pipe, if there's a foot available that would be ample. I'd go for a 110mm pipe anyday over a macerator. 110mm pipe is more fit and forget, done properly the chances of it blocking are a lot less than chances of Macerator problems.....

Thank you for this, it seems a bit obvious when you point it out. Inevitably there are few systems of any sort that aren't better off the fewer components they're made of which can go wrong.

I also obviously did my maths wrong but think the downstairs W/C is actually achieveable without saniflow anyway.

With regard to a new boiler, any suggestions about my main idea for a combi boiler + megaflow and a wet underfloor heating system downstairs, normal (but new) radiators upstairs for a single bathroom, 3 bed semi-detached?

 

[muggles]

Avoid a macerator if at all possible, they're hateful things that make a lot of noise and are just hideous when they break down and you've got to deal with the mess.

I fail to see, in a 3-bed house, why you think you want a combi AND a Megaflo (also known as an unvented hot water cylinder - Megaflo is a brand name for one of these types of cylinder). If you get an UV hot water cylinder you would just have a regular boiler, a combi would only be needed if you did away with any kind of cylinder altogether.

Both Combi and UV systems are reliant on a good flow and pressure of water from your mains, so you need to get this checked before you proceed. Combis require less than UV cylinders as a general rule, although it does rather depend on what you're trying to run. If you have the available cash and water supply I'd recommend a UV cylinder and regular boiler over a combi, although your house should run adequately on a combi. The advantages of the cylinder are that you have stored hot water so it's still there if the boiler fails, electric backup, and you can install a secondary loop for near-instant hot water to all outlets in your house. More expensive to run, but more convenient. My preference is for OSO Super S cylinders over Megaflo cylinders, the Megaflo ones are good but have had their share of issues and are relatively expensive.


Measuring flow and pressure - flow can be measured using a bucket of known capacity and a stopwatch, measure in litres per minute. It's best, if you can, to get someone to help with a second bucket at a second outlet measuring simultaneously, normally kitchen sink and outside tap, as one tap alone may be limited by it's capacity to pass water and give an incorrect readond. Pressure requires a gauge to be used, which is available from all good merchants and will normally have a 3/4" BSP thread connector that will fit your outside tap if you have one. You need to find both static and dynamic pressure.