Thermal store combi boiler, hot water flow rate.

[Matt0029]

Can anyone tell me the hot water flow rate on a thermal store combi boiler? As opposed. To a 40kw combi that will deliver nearly 16litres per minute. And any recommendations for a good thermal store boiler thanks.

 

[Brambles]

Unless I am misunderstanding your point, I assume you mean a combi boiler with an integrated hot water storage facility behind it all mounted on the wall?

If so, a combi like a Valliant 938 with a shift load cylinder (Valliant’s term not mine) will only deliver hot water at the incoming flow rate. The shift cylinder, if so configured, holds around 1 minutes worth of hot water at a delta T of 35 degrees. The pump in the shift cylinder is to circulate stored hot water not to deliver it.

I am not recommending the Valliant, just using it as an example ( I don’t really like large Combis’).

However, from my experience, again using the Valliant as the example, unless you have a consistent cold water flow at the boiler inlet of at least 23 lpm the boiler won’t perform to specification.

A common issue I come across large properties, where a Combi should never have been installed, is :

The toilet being flushed, hot tap at the basin turned on, then the shower - cold flow to the boiler dropping well below that required for maximum output. Unhappy customer who really wants a “hotel quality” shower.

 

[Matt0029]

Thanks I do mean a wall mounted boiler with internal thermal store. Are you saying they only offer about a minutes worth of stored hot water?

 

[Brambles]

The only boiler with a thermal store that I know the idiosyncrasies of well is the Vaillant 938. The store volume (shift load cylinder) is 15 litres. With the right inlet flow rates the boiler will deliver 20.5 litres/minute at delta 35 degrees or 13.2 lites/minute at delta 42 degrees.

We use them in externally installed, heated modular units in London coupled to a pumped accumulator and water softener. Very well suited to three storey terraced houses where internal space is at a premium in areas of low pressure and flow.

Others with know better, but I am unconvinced of the benefit of the storage module if you can get the flow to the boiler to allow it to deliver hot water at full capacity for 20 minutes.

 

[Gasmk1]

The viessmann111 has a 60 litre store the 222 think has 100 litre both give amazing flow rates never fitted the 222 but fitted a couple of 111 and have been very impressed by them

 

[ShaunCorbs]

viessmann 111 will give around 18lpm

viessmann 222 with give what you put in eg 25 lpm you get out 25lpm its a good piece of kit