New boiler advice, standard or combi

[Elkato531]

I'll add one more comment because I respect Madrab's knowledge and experience.

Madrab, I assume you have upgraded from a much lower capacity vented hot water cylinder that was probably there previously and would not have met your current requirements. For my own house, I decided I couldn't spare the space for a large unvented but wanted good shower performance so went with a combi despite the downsides which never really became an issue. The kids have all now left home and I'm quite happy not to have an enormous unvented cylinder.

As far as the OP is concerned, they probably have (and I'm guessing here based on experience of the many properties I've visited) a small, vented hot water cylinder, a mixer shower with very poor performance possibly boosted by a pump which they have had problems with, and maybe an electric shower that is at best adequate but disappointing. They need a new boiler. Can we suggest a possible solution that will give them improved hot water performance and maybe free up extra storage space in a small house where space is at a premium?

 

[Madrab]

Madrab, I assume you have upgraded from a much lower capacity vented hot water cylinder that was probably there previously and would not have met your current requirements. For my own house, I decided I couldn't spare the space for a large unvented but wanted good shower performance so went with a combi despite the downsides which never really became an issue.

Luckily no - we have a specific utility space for the cylinder/pump/etc so it has always been an unvented - property is a '96 build. It was an old LP Accolade and since upgraded to a larger Ultrasteel. I am also lucky to have very good mains supply in both pressure and flow and can run multiple showers with a minimal impact to output.

Couldn't agree more with you though that a combi can certainly meet a families requirements if they are happy to manage it's limitations, especially where some houses have real storage space issue and more can be gained by removing a cylinder and the CWSC. I have installed combi's for those exact reasons and the clients are happy to work with their limitations when it comes to HW delivery.

I think the crux here is the OP's reasoning behind the upgrade - is it to gain the extra space by removing the cylinder and the water storage that is presumably above their heads, or not. If we knew that then I think a lot of the to'ing and fro'ing could have been avoided. If it is for the space then a combi would certainly be the preferred choice to provide mains HW and recover that space but if space isn't the issue then I would suggest the more flexible of the 2 would be to retain the stored HW. If the mains allows, which may also be a consideration for a combi, then an unvented could also be considered.

 

[fixitflav]

Be nice to get the OP's reaction to this interesting discussion!

 

[stem]

That's an advantage for DIYers, because they can replace or fix those parts themselves. Unlike combi's which require the attendance of an RGI.

Maybe for the likes of you and me and others who frequent sites like this but not applicable to the majority of homeowners.

Agreed. But this is a DIY forum.

 

[Elkato531]

Its also a site where people seek advice. If all they get is the likes of Bloomfield with an axe to grind, they are not going to get the complete picture in order to make an informed decision.

 

[Harry Bloomfield]

Its also a site where people seek advice. If all they get is the likes of Bloomfield with an axe to grind, they are not going to get the complete picture in order to make an informed decision.

I don't have an 'axe to grind', I have just seen so many friends be talked into having their open vented converted to a combi, then regretted it after.

I've also had visitors stay here, who have only come across combi-systems, curious and impressed, at the speed of delivery, and flow of my stored hot water system.

 

[camerart]

Hi N,
My system is 1986, and aprt from flushing out and reinhibiting, the only thing that has broken has been the pump, and I changed the starting capacitor, for a few pound, and am still having hot baths
Think twice before changing.
C.

 

[fixitflav]

My system is 1986

What system do you have?

 

[Harry Bloomfield]

My system is 1986, and aprt from flushing out and reinhibiting, the only thing that has broken has been the pump, and I changed the starting capacitor, for a few pound, and am still having hot baths
Think twice before changing.

I would suggest, you have been very lucky then

My system is perhaps a couple of years older than your own. On it's third heat only boiler - first had nowt wrong with it, just convinced to swap it for a more efficient one. The 'more efficient one' caused constant issues, and faults, a year or two back I became fed up of it and swapped it for a new one.

A new pump, 3-port valve, and controls, were fitted as part of the package of the second boiler.

Over the years, we have had numerous 3-port, spring return actuators fail, but never a single valve.

I have now swapped out the spring actuator, for a MOMO type, as I liked the less mechanically stressful design, of no spring.

At the last boiler swap, I upgraded the controls to a fancy electronic system, taking into account outdoor temperatures, and setting the boiler output to match the heating demand, which it always has. perfectly.

So generally, the most frequent point of failure, is the 3-port actuator. An easy fix for me - I always keep a spare to hand. Heating is never off for longer than 30 minutes.

 

[Elkato531]

I don't have an 'axe to grind'

But you're blaming the product when its the bad decision and/or poor installation which is the problem. There are pros and cons as I've said before and people should be properly informed of all the advantages and drawbacks of each option and consider them against their particular priorities.
What they tend to get though is. 'Never get a combi, my mate had one and he's not happy with it.'
Don't forget also that people will focus on the negatives. My wife will occasionally mention that it takes a while for the hot water to reach the cloakroom basin. What she doesn't mention, though, is that she can jump into a powerful shower everyday, that we have potable water at all outlets and that she has room for a dressing table where the airing cupboard used to be.

 

[Harry Bloomfield]

Don't forget also that people will focus on the negatives. My wife will occasionally mention that it takes a while for the hot water to reach the cloakroom basin. What she doesn't mention, though, is that she can jump into a powerful shower everyday, that we have potable water at all outlets and that she has room for a dressing table where the airing cupboard used to be.

Go on then - the negatives???

 

[bernardgreen]

Failed pump on a combi, requires GasSafe person to dismantle the boiler to get to the pump to replace it.

Failed pump on a vented heat only system, the pump can be replaced by any competent DIY plumber,

Low pressure in water supply ( burst main ). several combi boilers refused to fire up.

 

[Madrab]

I think we all need to agree that there are pro-and cons for both combi and stored HW system types - if that wasn't the case then everyone would still be using open vented gravity systems with electrically heated HW cylinders. Time marches on, along with CH/HW system development following on and there are now numerous different options that a homeowner can consider that all have their place. it's the job of the professional to consider the clients requirements, site conditions etc and then suggest the best suited option(s) to deliver those requirements.

Instantaneous combi HW has a well earned place, as do indirect open vent cylinders/unvented cylinders, under sink electric heaters etc and any of these, IMO, can be the better option depending on the end users requirements, which brings us right back to the start of this post -

@neza - can you please come in on this, as it's your post - and clear up what is driving your considerations when it comes to what you need as far as a CH/HW system is concerned.

 

[fixitflav]

@neza - can you please come in on this, as it's your post - and clear up what is driving your considerations when it comes to what you need as far as a CH/HW system is concerned.

And maybe something about the house layout, as that might affect the choice

 

[fixitflav]

she can jump into a powerful shower everyday

I wasn't going to come back, as you make fair points, but just want to add that you can have that with a mains-pressure HW cylinder