Advice on Combi Boiler

[richy92]

Hello - I was hoping for some advice and opinions on a new combi boiler

I currently have a 3 bed semi with a myson orion boiler (it isnt a combi) - the boiler was installed around 1989, hasn't given any problems and is still working fine. Due to the increase in gas prices it is time to change to something more efficient. I have a header tank in the loft, hot water tank in the bedroom, 1 power shower and eight radiators (4 doubles).
I have done a lot of reading and think I have a basic understanding of central heating systems, I am also a competent DIY plumber.
I am a little worried about losing my nice shower, its only a cheap thermostatic model that runs from the hot water tank, but it really chucks out some water, looking on the web I believe its around 14ltr min. When I change to a combi I don't want to end up with a poor shower - so flow rate is important.
I would like the new boiler fitted in the same space (it isn't essential but preferable) 400mm wide.
The 14 ltr min flow from the shower is a mix of hot/cold - so I guess 10 ltr min pure hot water from the combi should be enough to match ?
I don't want to go crazy but I may do a loft extension in the future so want some spare capacity. I'm not too worried about cost, if it only lasts half as well as my current boiler I would be happy.
I was looking at this :

WORCESTER BOSCH GREENSTAR 36CDI GAS COMBI BOILER
It has a great flow rate and looks like enough capacity for 10 radiators or more - they get a good rating and have a good warranty.

Any advice would be great - thanks

 

[Knappers]

Hi richy92,
You don't need to worry atall about the heating capacity of a combi boiler (you'd be able to heat 3 houses with one) the pressure and flow from a combi will usually be better than a gravity fed system but it is worth checking your mains flow from kitchen tap. Getting a boiler that can heat more than you have is pointless.
Usually 30kw is plenty but if better flow is what your after then itay be worth stepping up to 35/36kw (wouldn't recommend any more of a step)
I would consider the Worcester 4000 but you can't go far wrong with any of the main brand boilers (worcester, Vaillant, baxi, Viessmann etc)

 

[Knappers]

You will need to change your pumped shower tho

 

[richy92]

Yep, I know I need to change the shower - it is a cheap Wickes version with the pump in the shower unit not a separate pump. It runs from the hot water tank in the cupboard and the cold water tank in the loft, so it is gravity fed, but also pumped to give a good flow. I will change the shower unit for a thermostatic mixer (no pump) as both hot/cold will be main pressure, I am hoping a decent combi and mains pressure will provide enough flow for a shower close to what I have currently ?
I considered the Worcester 4000, it looked good to me but is too wide to fit in the space I have, that's why I was thinking of the CDI as it is a little slimmer.
If the boiler size is different I will need to remove a shelf unit to fit it, it isn't impossible, is there much difference between the 4000/36cdi ??
If you were fitting a new boiler in your own home and cost wasn't a big issue, who would be your favourite manufacturer ?

Thanks for your help

 

[Knappers]

It wouldn't be helpfull for me to share my thoughts on boiler brands and their pros and cons.
Cdi is a good boiler.
I'd go with worcesters 'easy control' as a must if fitting smart control's to worcester boiler.

 

[PETE 123]

Or leave everything as it is and get a heat only boiler.

 

[richy92]

It would be much easier to replace it with a heat only boiler, but I don't want to heat a tank of hot water just to wash up dishes. I should make a big saving by only heating the water as I use it. An additional benefit is recovering a load of floor space in the loft, I have two large cold water tanks up there at the moment. There must also be a big difference in efficiency, I have no idea what the rating for my old Myson Orion is, but I doubt it's anything like the current models.
If it wasn't for the increase in fuel costs I might be tempted to leave it alone, its worked fine for over 30 years now and shows no signs of any problems.

Thanks for your help

 

[Knappers]

Easy control with weather comp will give savings as well as added comfort by keeping room temps more consistent.
The sales literature will state 1-2% saving but I think that a well setup system would allow you to run house a little cooler without compromise.
I'd say 5-10% is easily achievable (based on absolutely no verified evidence and entirely just my opinion)

 

[richy92]

Thank you - I have another question - Will I need to have my gas feed upgraded, the current Myson boiler has a 15mm gas connection that I believe runs right under the floor of the house (not easy to access), should I have this upgraded to a 22mm pipe running around the outside of the house ?

I would think it is better/safer to have the pipe running outside the house rather than under the floorboards, what do you think ?

 

[ShaunCorbs]

22 maybe 28mm depending on length and run

 

[gmartine]

The Orion is about 65% efficient so not great but actually the efficiency case for heating a water store compared to instantaneously water heating isn't always as as clear cut as you might think. Anyhow seeing as you want the loft space a combi is the way to go.