Vaillant 837 / 937

[diy_darren]

Next year I plan on replacing my current gas boiler with a combi capable of running a decent pressure shower and not being too badly affected by someone filling the sink or washing their hands. There are many boilers I could choose, but I like the Vaillant boilers (neighbour has one).

Can someone confirm that the 937 is basically an 837 with the extra 15 litre storage unit?

The storage on the 937 gives it the advantage to start with, but without a huge hot water demand I'm concerned it will be preheating water unnecessarily (assuming the 15l storage is preheated?). In the winter that's OK as the heating will create demand, but pretty wasteful in summer. I read somewhere that the storage feature can be temporarily disabled on the 937, is that correct? Does that make it behave like an 837?

 

[gas4you]

Yes the 937 is the 837 with 2 7.5 litre storage tanks behind it.

Unlike other storage combis, this does not 'use the store first', but takes some of the stored hot water and blends it with the combi heated water to give it the 20 l/m flow.

Sensors detect the hot water flow and use either one or both of the stores to deliver depending on the flow rate.

I am not complete techie on this yet so do not know the exact ins and outs of the workings.

 

[diy_darren]

As it mixes the stores with water to maintain the high flow it'll be even more waste for a house that doesn't have a high hot water demand. Looks like I'll be going for the 837 then.

 

[gas4you]

Doesn't matter how it mixes it, you will still use the same amount of hot water

Filling a bath with mixed hot is the same quantity as direct combi hot, only it is filled quicker.

 

[diy_darren]

Doesn't matter how it mixes it, you will still use the same amount of hot water

I realise that, my concern is that the 937 pre-heats the 15l storage while the 837 doesn't. Without a high hot water demand (in summer) I'd be wasting energy with a 937.

 

[Agile]

The storage is well insulated and the heat loss will be very small and in any case is fueled by cheaper gas.

Compare that with so many houses which have an old copper hot water cylinder and only a badly fitting red segmented jacket and are heated by electricity.

Tony

 

[gasmanuk]

To answer your first question though, yes you can turn off the preheat.