On 03/03/2021 13:58, Dave Plowman (News) wrote:
In article ,
rick wrote:
After another 6 days with no heating ..... boiler repaired under
maintenance cover (burner, burner door, seal & electrodes), but thinking
it's time to look at replacing .... becoming pretty unreliable.
Its now 22 years old.
Its a 30kW Heat only wall mounted gas condensing boiler - connected to a
pressurised thermal store.

I need a standard/Heat only ..... can't use as system boiler (as thermal
store control need to manage pump)

Is that the case today? No thermal store can be used with a system boiler?
When I did a self install quite a few years ago, Viessmann had an
incredibly helpful technical advice guy in the UK. Seemed to know
everything.

Just that system boilers being the norm, may be far better value due to
economy of scale.



Not tried Viessman .. if you have a name to contact be happy to try them.

The reason I can't see how to use System boiler is that thermal store
operates the pump to 'stir' the store when you are drawing off DHW .....
otherwise heat exchanger gets cool quickly and you lose hot water.

Works really well ..... but with a System boiler the Boiler controls the
pump, and therefore the Thermal Store controls can't operate a 'stir'

When I put in the system teh company specified a HEAT only boiler for
this reason.
The thermal store installed is not changing, and heating company state I
should still use a HEAT only boiler.

I had thought of installing Vaillant but they advise only their system
boilers can be connected to a pressurised Thermal store not Heat only.
When I asked them how do I get the pump to stir the store - that was
beyond their experience and could offer no solution.