This has been discussed before, in particular the fact that most gas boilers need a cold water supply. The Rinnai Infinity 11e has been mentioned before as a boiler that will take, say, 36 deg water and boost it to 50 deg water for DHW. This is great when in the shoulder seasons one doesn't want to batch burn a Wood Burner but the water at the top of the TS isn't quite warm enough for a decent shower. At the small DeltaT I mention, ie 14 deg difference, the Infinity will deliver 20 litres/min at 50 deg C.

Anyway the point of this post is that this is no longer theoretical for me. We have decided to install one and it will be the Infinity 11e at just under 600 euro (I live in Italy), unless anyone has a suggestion for an alternative (cheaper!) boiler. It has to be mounted outside as I don't have space inside but it will be in a bespoke 'pretty' house as I am under orders on this and it will never be used when it is near freezing so an 'internal' boiler might also work.

The purpose of this is to prevent me batch burning up to 10 time a year; more importantly it will provide me with certainty during the shoulder seasons (when I don't need to space heat) that my in-laws (who live in their own apartment within my house) will have DHW if I am away. I can't go away during the summer due to work or during winter as I must batch burn daily.

So:
1/Any recommendations on a cheaper appropriate boiler?
2/Should I be looking to bypass and drain down the boiler when it isn't needed, ie summer and winter?
3/Am I right in thinking that this Max 22kW boiler will use about 1.6kg/hr if flat out?
4/Any other thoughts to ready me for a potentially stuck in their ways gas engineer who will be giving me a quote - ie any thoughts to help me become an intelligent customer?

Rinnais are v good.Work straight out of the box, no grief.....

Could you just fit an immersion element to the store?

I've used a Vaillant combi to post-heat a TS output. This is what I emailed to my gas safe installer when I replaced an old Ariston Microgenus with a Vaillant Ecotec Pro 24:

Vaillant have said "all ecoTEC and ecoMAX/2 combination boilers can
accept inlet water temperatures of up to 60°C" but go on to say "there
is currently no industry wide WRAS approved method of connecting such
systems to a combination boiler"

- this second bit is in reference to solar pre-heat cylinders, and
appears to be a reference to legionella control. However my system
uses a thermal store instead of a preheat cylinder so
would appear to be OK with regard to this (would fall into the low risk
category for systems with a capacity of less than 15 litres of water,
since it's essentially just the heat exchanger capacity on the thermal
store).


If you do happen to go for the Ecotec Pro 24 (I got mine for about £600 new, but you can often pick them up cheap secondhand for £150 or so on eBay - but do that quick before the heating season starts and they all get snapped up!), then it's possible to upgrade its DHW temperature control by adding the DHW outlet temperature sensor from the old (very closely related but a little higher spec and discontinued) Ecotec Plus 24. The extra sensor is about £5 as far as I can remember. This worked a treat and was automatically recognised and used by the control board (which is the same one as used to be used in the "Plus 24".