Is there a requirement to upgrade the controllability of the individual radiators at the same time the boiler is replaced? In practice I mean fitting TRVs but I would rather defer fitting them until a later time.
Is there any other work that is likley to be insisted upon?
Unless you are doing this directly through building control, I would not have thought so.
GasSafe fitters self certify for Part L and gas purposes so whatever the fitter is happy doing.
ICBW but my belief is that the only requirement is to have boiler interlock, so that the boiler shuts down when all demands are satisfied. This usually needs zone valve(s) and separate thermostats for space heating[1] and HW. What have you currently got?
[1] One whole house room stat should suffice
Currently a lump of cast-iron in a lean-to feeding S-Plan pipe work. Independent control of DHW and CH.
I want to replace it with a wall-mounted combi in the kitchen. Shouldn't be too difficult for the engineer, as cold feed, feed to hot taps, 22mm gas with prob four 90deg bends when complete, and rad flow & return are all at floor or under-floor level at the proposed site.
Is that gas supply likley to be OK for a combi? Four bed semi, one bathroom and a frugal owner (me) who won't mind it being a little under-powered?
Best practice would say that the TRVs are required. But is a new boiler a new system?
May be a problem when you come to sell it. I would allow for the cost of putting in a new boiler and tanks when making an offer on the house,
That would, of course, be your prerogative. I'm sure someone else would take a more practical viewpoint.
Of course, after 5 years it might well need replacing in any case!
It's unlikely, although not impossible. Combi is likely to be ~3 times the power of your cast iron lump, and existing pipework may drop too much pressure, in which case it will need replacing with a thicker pipe, possibly with a more direct route and/or fewer elbows. (Often, pipework is already undersized for existing boiler, since back when this wasn't an issue.) If you can give the pipe length, diameter, number of elbows, and number of formed bends, someone can work out the max boiler power it will support. Get's more complicated if there are any other gas appliances T-ed off it.
You can't get away with low pressure on gas inlet - it will fail the commissioning test, and it will fail any landlord safety check (and the boiler might not work properly). You could use a lower powered combi, which might get you inside the max power your existing pipework supports if the current pipework is close.
A new boiler requires bringing controls up to current regs. The regs do not specify needing TRVs, but you do need something better than a single roomstat controlling the whole house, unless the house is very small. Zoning and/or TRVs are options, but the precise method is not dictated. The other requirement is that the boiler must switch off when no zones are calling for heat - it's not allowed to continue heating a bypass loop, so you can't use only TRV's - you need some type of interlock to shut boiler off if they all close.
It's quite short, 11-12m
ISTR that each 90deg bend increases the effective length by half a metre so let's say 15M. This appears to be the top limit for a 32 kW boiler
0.5m for an elbow or tee, 0.3m for a "Pulled" bend or swept 90.
You have omitted a key detail, the pipe diameter.
15m effective length, gives a maximum flow rate of 1.1m^3/h for 15mm, and 3.4m^3/h for 22mm.(the former would be inadequate for any combi, while the latter good enough for almost all of them)
Conversions available here:
Sorry John I was embellishing my previous post where I gave the diameter (22mm) but omitted the length.
If the pipe to the boiler location is only 15mm it will probably need to be upgraded to 22mm.
Are you getting rid of your HW cylinder (not recommended!) and relying on 'instant' hot water for all your HW requirements - bath, shower, washbasin, kitchen sink, etc.? If so, you won't need your S-Plan zone valves any more - and you can control the CH side of the combi with whatever stat currently switches the CH zone valve. [Unless, course, you wanted to re-deploy the HW zone valve in order to create two separate CH zones].
The alternative - preferable in my opinion - is to keep the HW cylinder and S-Plan system and drive all of that from the CH side of the combi - and just use the combi's instant hot water for the kitchen sink.
Others, such as Drivel - wonder where he went? - may not agree.
It rather depends.
In the old house I took out the tank and put in a combi, and for that house it was a good option.
I wouldn't do it here though
My apologies - I missed that.
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