Large extension added to my 3 bed property. Combi has been a pain in the arse and now won't cut it with 2 main bathrooms.
My question is should I go for a system boiler with an unvented cylinder or get a conventional boiler and have pressurised ch and again an unvented hot water cylinder?
Plumbing in the extension hasn't started yet and I plan to put the unvented cylinder in the gurage.
My plans were for the system boiler but I met a plumber who said to go conventional.
A conventional boiler with a cold water tank and a hot water cylinder allows the use of an immersion heater to provide hot water if the boiler fails. Simpler boiler with less to go wrong.
Ultimately it is up to you to decide which alternative you prefer. I am just about to go to a property which has a system combi boiler that is not working, so I will be cold and have no hot water (kettles apart) until I fix the problem.
A system boiler implies a conventional system. You have a choice of unvented, vented or thermal store.
I went for the thermal store as the cylinder isn't pressurised so doesn't need inspection and testing while still having high pressure hot water.
TBH I suppose I just did the first inspection and test of my pressurised cylinder in 16 years after replacing all the pressure bits... :-)
Personally I'd still go for a pressurised system
Thermal store almost as good.
Combi = f****ng awful unless you get a huge one
Combis are good for a small house or flat. They can only realistically supply a single outlet with hot water.
They are usually much larger than needed for heating so often cycle on and off.
My first experience of a combi was having to turn the shower up to blast otherwise the combi kept cutting out. £££waste.
NT
A bigger combi might be all you need (and probably the cheapest option), but a conventional boiler with an unvented tank and immersion heater back up is the "Rolls Royce" of systems from the point of view of HW supply with back-up IMO.
Tim
Can depend on location. Thermal store in old house suffered from major scale up in the small bore pipes that run through the thermal store to provide HW. Filling a bath ended up being so slow that water was cooling down faster than hot water being supplied. Just barely acceptable for shower or washing up. Probably worse than a combi. A Water softener may have helped but there wasn't one fitted,
Might have been a pain to do but I don't see a problem with running a descaler through the coils.
I think anyone who doesn?t fit a water softener in a hard area in a property they expect to inhabit for a decade or more is a numpty
The damage done to shower fitments especially is massive. Not to mention the internals of a complex hot water system
I think IF you are going to upgrade a DHW system fitting a softener is probably step 1. Even a combi will scale up eventually.
I think the difficulty is the problem.
Well technically it had one of these chemical cartridge type softeners
replying to Tim+, Darksyphon wrote: Thanks for the replys. The only thing I'm wondering is if I need the central heating side pressurised too? I like the idea of not having any tanks. But that means more gear....another pressure vessel. Just wondering if the extra reliability of a conventional boiler is worth having to add all the things seperatly that are now inside system boilers. I'm not bothered about the cost just want the best system that is reliable. Not looked into Thermal stores. Will have a read
reliability is more about implementation than design.
If converting from a combi, system boiler makes sense since your won't already have a separate pump or the separate paraphernalia associated with a sealed system (since they are all in the combi).
Ultimately you will have the same major components, its just the location of them that changes.
Note however you may be able to implement more sophisticated controls with the system boiler, to give things like split temperature operation[1] or weather compensation[2], which are harder to do with heating only boiler usually.
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