It should read, "you will need to replace the hot water storage cylinder
with a part L1 compliant one (or better) to comply with the building regs"

No it shouldn't. There is no requirement to replace the hot water cylinder
with a compliant one when changing the boiler.

Read the following. Paraphrased,

1. When replacing the boiler, you must fit an efficient one, and update any
controls and provide fully pumped circulation and boiler interlock. There is
no need to change the hot water cylinder.

2. When replacing a cylinder, you must fit an efficient one and update any
controls and provide fully pumped circulation and boiler interlock. There is
no need to change the boiler.

Note that the actual boiler efficiencies suggested below have been
superceded with a new table since publishing of the original Part L1.

Christian.


2.3 Reasonable provision where undertaking replacement work on controlled
services or fittings (whether replacing with new but identical equipment or
with different equipment and whether the work is solely in connection with
controlled services or includes work on them) depends on the circumstances
in the particular case and would also need to take account of historic value
(see paragraph 2.9 et seq). Possible ways of satisfying the requirements
include the following:-

b) Heating boilers. Where heating boilers are to be replaced in dwellings
having a floor area greater than 50m2, providing a new boiler as if for a
new dwelling i.e:-

(1) In the case of ordinary oil or gas boilers, providing a boiler with a
SEDBUK not less than the appropriate entry in Table 236, together with
appropriate controls following the guidance starting at paragraph 1.36. (In
the case of replacement boilers installed in the period up to 31 August
2002, it would be reasonable to provide a less efficient boiler provided the
heating controls comply with specification HR2 or HC2 given in GIL 5937;

(2) In the case of back boilers, providing a boiler having a SEDBUK of not
less than three percentage points lower than the appropriate entry in Table
2;

(3) In the case of solid fuel boilers, providing a boiler having an
efficiency not less than that recommended for its type in the HETAS
certification scheme.

c) Hot water vessels. When replacing hot water vessels, reasonable provision
would be to provide new equipment as if for a new dwelling following the
guidance beginning at paragraph 1.43.

d) Boiler and hot water storage controls. So that replacement boilers (other
than solid fuel boilers) and hot water vessels can achieve reasonable
seasonal efficiency, the work may also need to include replacement of the
time switch or programmer, room thermostat, and hot water vessel thermostat,
and provision of a boiler interlock and fully pumped circulation. Section 4
of GPG 30238 gives more advice on how this can be done.