Megaflo with a combi boiler

[Mamps]

Hi
I'm in the process of major house renovations. Its a 3 bed semi with 1 bathroom, but now I will have a loft ext with ensuite and an kitchen extension with utility room. So, originally I was going to go for a combi as I like the idea of instant hot water instead of waiting for a tank to heat up, but realise that for more than 1 bathroom, there with be flow loss if more than 1 shower is in use. So megaflo it is. The next decision is the size of the tank. I heard/read some stories of the water running out quickly as it is pressurized, so was going to go for a 250 cylinder, but for 2 reasons, am now going for a 210. 1 is that although it is a 4 bed house now, only I live there at the moment and that a 210 will still be fine for a family if I ever have one or if one moves in., the 2nd reason is because the cupboard the megaflo will go in, is 1300mm deep and 700mm wide and I thought it would be better for me (for storage purposes) and better for a plumber, if the boiler sat directly above the megaflo - although plumber would have to get on a ladder, its directly in front rather than, if I put it on the wall on the right (outside wall), not much room to swing round. 210 is 1500 high so still room for a boiler above it. I would be interested to know what plumbers thought about my reasonings here. My next decision is the actual boiler. As I was going for a megaflo, I thought I would then have a system boiler rather than a combi, but I've seen somewhere that combis are better stronger boilers and so its better for me to get a combi which will run my central heating better. i have 8 large radiators, 2 towel rads, plus I will be putting 12m sq water underfloor heating in the extension (100m hose). I also read that I can have only my 2 bathrooms using the megaflo water and then kitchen, utility & cloakroom can use the combi for hotwater. Is this true and how much more effort is it for the plumber bearing in mind there is no pipework as yet to the kitchen, utility, cloakroom.
Thanks
Mamps

 

[Mamps]

Forgot to mention, another option is to keep my existing boiler. Its a Potterton suprima. Never given me any problems except for recently, it switches off for no reason and I have to press the reset button. Has been regularly doing that recently. Is it worth having it fixed and keeping it? Boiler position will be moved anyway, so thinking I should just replace it. Its 10 years old.

 

[gas4you]

It sounds as thought the pcb may need replacing. Depending on who fixes it could be up to £320.

Is it worth it for a 10 year old boiler?

Only you can decide that point.

Also moving an old boiler can be problematic apart from complying with current regs perhaps.

 

[Mamps]

Thanks Dave. So the question now is system or combi boiler? and if i have a combi, do I split the kitchen/utility/cloackroom to use combi direct and the bathroom and ensuite shower to use the megaflo...

 

[kevplumb]

no reason why not

done a few it works well

 

[Mamps]

Ok, so if I do have a combi and a megaflo, will the water in the cylinder be heated by the combi? so i'll still be having an indirect cylinder? I don't want to be using electic to heat the water in the cylinder as this would work out expensive in bills.
Also, its the splitting of the water (only bathroom & ensuite water from cylinder) be a very big job for the plumber? The new megaflo and cylinder will be positioned in the utility room next to the new kitchen. Bathroom is directly above on 1st floor, then there is a ensuite above in loft.

 

[kittedup]

Not a hard job to split the output on a combi.

You are correct you need to have an indirect cylinder which will be heated by the combi.

If it helps just think of the cylinder as an extra radiator that the combi will heat

Ted

 

[Mamps]

Yes, that helps. Thanks Ted.

 

[mysteryman]

As you are using an unvented cylinder, you may as well use it for all hot water, and fit a system boiler.

Choose a quality one with built in diverter valve, weather compensation and timing.

 

[Mamps]

The reason I was think of splitting, is bcause originally was going to have a 250L cylinder (for a 4bed, 2 bathroom house). Now am having 210L and am aware that megaflo water runs out quicker than gravity fed cylinder because the flo rate is quicker hence giving a lovely powerful shower. I figured it would be useful to have especially the kitchen on direct combi water so there would be no risk of the water running out for showers.

Another question I have about combis and ufh - i was told a while ago, that combis can't handle water ufh so well because of the amount of water flowing through. Is this true?

 

[mysteryman]

No, it isn't true.

You can add ufh to any boiler. The best ones have add-ons by the boiler manufacturer which will give the best possible control. Don't buy the controls from the ufh manufacturer - they can't interface with the boiler.

 

[mickyg]

just remember some important things.
Without decent water pressure/flow the whole plan is no good.
Having a combi AND a cylinder with all the associated controls increases the number of mechanical/electrical components and therefore the probability and quantity of faults you will suffer later down the line.
Personally I'd stick with a system boiler, i think the combi boiler idea is overkill.
Get a cylinder with a decent kw rated coil and wire the system as priority hot water, that way you'll very unlikely ever run out of hot water.

 

[mysteryman]

... and weather compensation to keep it condensing.

 

[DIYhandy]

A neighbour had a Worcester Bosch Highflow 440 combi fitted. It can do two showers easily. It is washing machine sized and floor mounted under a worktop. It is very impressive, belting out hot water. He said there is a more powerful version made, the same size as the 440. I don't know the model number. That may be the best between the cylinder and combi.