Back boiler to combi

[Belboz]

johnad - I am not a plumber so will leave the experts on here to advise you regarding the actual pipework.

However, I am aware of the combi v back boiler/cylinder arguments.

There are pros and cons for both and it all comes down to individual choice.

I have a back boiler and cylinder system. The cylinder is lagged and in good order. The back boiler is serviced annually. It is more than enough to meet my needs for hot water consumption and heating. However, the cylinder does take up space and the back boiler is less efficient than the newer combis (thus more costly to run) The main reason I have not gone the combi route is because I know I have an immersion back up in case of a failure. That was one of the main deciding factors for me.

Your situation appears to be that you have had good experiences of combis (not everyone has) and the hot water delivery rate has been fine for your needs. Your current system sounds like it may need some extra money spent on it if you keep it (possible new cylinder) and, of course, it will be generally more expensive to run [being less efficient] For you, immersion backup may not be a main factor.

On the other hand, you will need to buy the new combi and have it installed. It is correct that some rads MAY leak and need replacing but possibly they will be okay. The rest of the work you will be doing yourself so will save labour costs [but still need materials]

SO...it comes down to whether the money spent on installing a new combi system and the subsequent recoup over X years (in energy savings) would outweigh the benefits of keeping your current back boiler and cylinder.

You have to add in the unknowns such as servicing and breakdowns as well as possible inconvenience if your combi breaks down mid-winter.

All in all, it's your decision and there are good arguments for both 'sides'.

 

[Razor900]

Ok, as someone that's done well over a thousand.........................

It's very unusual for the rads to leak after sealing the system with the exception being old Servowarm units which are now thankfully rare! The valves can week from the spindles but they can usually be nipped up.

I'd fit TRVs in the bedrooms and kitchen and not bother with the rest.

Yes, you do need to get a flow and return back to wherever the boiler is going, preferably from the existing 22mm pipework. If you only have 7 or so rads you can sometimes get away with teeing therm off an existing 15mm rad but it's really not recommended.

usually the cold main would be looped into the bath supplies in the airing cupboard or loft and the hot would just be capped in the airing cupboard or if access is good the remove as much unneeded pipework as you can to prevent deadlegs that can breed nasties.

And make sure the old vent pipes for the water and heating are done away with lol!!

 

[johnad]

So if the only lightly leaks I may get will be from the rad valves I have no problem replacing them all when its drained down this was something I was considering anyway.
The house only has two rads upstairs + a towel radiator in the bathroom
And two rads downstairs lounge and kitchen so it's only a small system
I was looking at it and it just looked easy to pick up from the kitchen rather than re run the existing flow and return from the boiler
Why is it better to be done in 22mm I thought a pressurised system was fine on 15mm as I said the one on my old property only has about 4 feet of 22 from the boiler ?
However I can do it its just that it involves taking half the floor up etc
The boiler is in the living room fireplace the hot water cylinder is upstairs on the other side of the house and the new combi will be in the kitchen at the back of the house so a bit of a nusence running pipes ?
Is plastic push fit pipe ok on a combi system ?
Many thanks

 

[OwainDIYer]

Is plastic push fit pipe ok on a combi system ?

Yes but not for the first metre (or see manufacturer's instructions) from the boiler. And not for gas.

 

[johnad]

I'm going to get some quotes for the new boiler and maybe see if the plumbers would advise and let me do some of the pipe work removal etc
And go from there
What would be a good combination boiler to get ? Any to avoid ?

 

[Dan Robinson]

Intergas
Atag
Vaillant/Vokera.

In that order.

Viessmann if you want to spend the rest of your life reading a manual.

Wooshitter Botch are to be avoided along with Ferroli.

 

[mogget]

It's possible for joints to let go when converting to a sealed system, one went at my place when it was pressurised. But it looked to have been soldered by a halfwit that didn't know what flux was so in my case the problem was the original 1980s installer, not the pressure in and of itself.

Proper low pressure taps seem to be getting rarer too, my kitchen tap was advertised as minimum pressure 0.1 bar but that's pushing it somewhat as the hot water flow isn't great. The world is moving on and my next hot water system will be mains pressure but I haven't decided in what form yet.

Dan's got a point about the turndown ratios, my boiler is one of the better heat onlys in this respect but still short cycles sometimes due to me not heating the bedrooms.

Anyway to get to the point I would say that combi vs tank is mostly down to number of occupants and personal preference more than anything, provided mains flow is ok.

 

[Dan Robinson]

For the record.... I have been moaning to manufacturers about turndown ratios for years now.

Boiler cycling boils my pish somrthing chronic. However there are times to pick your battles when it comes to a bog standard boiler swap.


In my professional capacity we do fewer combi boilers than system/heat only boilers. And when we do a combi conversion we sure as hell make sure the customer is aware of the limitations of hot water delivery. Most however, want storage space and decent showers. Something a combi boiler will do much more efficiently than a 12kW HXi and a booster pump.

Perhaps Mr green would like to comment on the turndown ratio of an Hxi?

Geminox are the best for these ratios, but the boilers are of course French


Vokera are leading the way with their new Mynute range.

Honeywell have released OpenTherm to the multizone market... So the technology will be getting a boost from all manufacturers especially with ERP kicking in soon. Low modulation has to be given more attention IMO for the next generation of boiler. Especially with new build insulation standards getting so high.

 

[mogget]

I don't know a great deal about erp yet but I think an awful lot of end users eyes will glaze over and they'll shout 'psychobabble' because a good portion of the population don't know that they don't know how to operate a thermostat

Seems to put a burden on installers from what I've read.

Will this mean that we'll all be forced into weather comp?

 

[Dan Robinson]

ERP is just more ****** thrust upon the industry by people in offices that get manicures.


It is scary how many customers refuse even the basic Party L upgrades. Give them a shiny sticker telling them the efficiency of their new system package (which will be a load of crap anyway as most are still running old rads and pipe work in poorly insulated houses with the stat cranked up to 30) and they will probably think it is another scratch card or something.

Honeywell still get tech calls about T6360's FFS

Imagine trying to explain to your average box slinger what a class 8 package is

 

[mogget]

I'm metaphorically scratching my head about why anyone would need to call support for one! That said my digistats are probably getting on for 20 years old and I think theyre modern

But not much point replacing them as I loathe programmable stats. If my boiler was on effectively continously with weather comp it wouldnt modulate down to the few hundred watts I need for the majority of the year. So I'd end up paying lots of money for controls and still get short cycling.

I hope I still have the option to have 'inefficient' controls in the future.

 

[bernardgreen]

Perhaps Mr green would like to comment on the turndown ratio of an Hxi?.

The J&S Reno 16 appears to modulate down to less than 2 Kw ( rough estimation ).

My shower is mains pressure with the hot supply heated by a secondary coil in the top of the hot water tank. ( custom made to fit the available space )

 

[Dan Robinson]

Yes, but your boiler is a ****box.

 

[Dan Robinson]

And according to my manual it is 3.75kW.


So more ill informed nonsense.