John Stumbles wrote:

Mains pressure
hot/warm water ---------
from thermal store | combi |
------------------+---| DHW |------
| --------- |
| -----
| | H |
| | TMV |-------
| | C |
| -----
| |
---------------------

To save potential complications from feeding the combi with prewarmed
water (which could in some cases be *hot*), you could do:


---------
mains cold | combi |
-----------------------| DHW |-------
--------- |
-----
| H |
| TMV |-------
| C |
-----
preheated water from store |
------------------------------------------

(with optional additional blending valve at the output as you suggest)

Or if you want to take advantage of the prewarmed water for the combis
DHW input you might need:

---------
mains cold | combi |
-------------- ---| DHW |--------
| | --------- |
----- | -----
| C | | | H |
| TMV |- | TMV |-------
| H | | C |
----- -----
| |
| |
preheated | |
water | |
| |
-------------------------------------------

Set the output temp of the first TMV so that it does not exceed the
maximum inlet temp on the combi.

Obviously you will use energy from the store faster this way and will
reach the point where the combi is supplying the bulk of the heat sooner
(and hence you may need to reduce flowrate to maintain temperature)

--
Cheers,

John.

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