What boiler for thermal store?

[M550344]

I have an existing coil based 300l thermal store and my plumber has said my Veissmann 19kw condensing boiler is not suitable as it does not the capacity to heat the thermal store and the fact that you cannot turn off modulation. He is recommending a Potterton Precision boiler. Do I need to change the boiler and if so is the Precision model the only option? Reason for new boiler is thermal store is not reaching desired temperture for ideal operation.

 

[Neil K]

What else is your existing boiler heating apart from the thermal store ie. How many rads and what sort of property have you got

 

[M550344]

12 radiators, detached 4 bedroom 2 storey home, fully insulated, new double glazing.

 

[Neil K]

19kw boiler is not enough to heat 12 rads and a thermal store. The make of the old or new boiler is irrelevant.

 

[IDCHAPPY]

How much heat does the thermal store need?

 

[stevetheplumber]

i would look for a 30kw boiler heat only to go with a thermal store

 

[Neil K]

How much heat does the thermal store need?

It needs to be preheated to 80-90 degrees c because you are using mains for your Hw just like a Combi. I would agree with Steve, that house definitely needs a 30kw boiler

 

[IDCHAPPY]

I was thinking 19kw sounded a little tight on the output

 

[M550344]

Both DHW and CHW are taken directly off the thermal store

 

[Neil K]

Are you saying all the rads come off the thermal store too? Is there a circulating pump beside it somewhere?

 

[M550344]

Yes all rads come off thermal store direct connect with Grundfos Alpha2 pump

 

[Nostrum]

I wouldn't be surprised if the thermal store was undersized also.

 

[Neil K]

Yes I've seen this set up before. Your boiler is definitely undersized pal.

 

[Bolty123]

Does your system not work as it is then? I think you would get away with it.

 

[Bolty123]

How long does it take to heat the store I mean

 

[M550344]

The first 5 mins of hot water is ok and the not so good. Radiators take a while to get up to 22c

 

[Gray0689]

Why have you got a thermal store in
Have you got a solid fuel boiler going in to it or just the gas boiler ?

 

[Bolty123]

Have you got your cylinder stat set high? 80 degrees at least?

 

[antdad]

Why have you got a thermal store in
Have you got a solid fuel boiler going in to it or just the gas boiler ?

Exactly...isn't the whole point of a thermal store so you can utilise more than one heat source, like solid or solar as well as gas?

 

[Mike Jackson]

A lot of new builds had thermal stores put in. mains pressure hot water without the need for a G3 registered installer and no need to get a discharge pipe to outside.

 

[Nostrum]

Not anymore

G3(3) embodies the previous requirement G3,and applies it now to all hot water storage systems. Its scope has been extended toinclude primary thermal stores.

What is it that you are running that is depleting the store within 5 mins? Power shower?

 

[DrainMedic]

CH and DHW are both drawn off the thermal store. Kind of like a HW cylinder in reverse.
The boiler should be big enough, given that the boilermate contains 2 3kW Immersions as a backup in the event of boiler failure, and they don't perform too bad without the boiler.
Slghtly off topic, but I shut down a boilermate last Monday and returned to strip it out on Wednesday and it was still red hot! They must be incredibly well insulated!

 

[Worcester]

How the *** do any of you know if the boiler is undersized or not without doing the heat loss calcs?
You don't even know how big the rads are, so you can't say if its big enough or not.
The Thermal store acts as both a buffer for the CH system and a DHW system
The fact that the boiler doesn't modulate is precisely one reason for adding in the thermal store.

The thermal store effectively does the modulation.

Talk to a qualified Heating Technician not a plumber / boiler fitter..

 

[Ermintrude]

Sounds like the coil in the store might be scaled up and unable to transfer heat as well as it should. Keep boiler swap store. Acv SLME and forget about the installer. Also have u got weather comp on the Vissman?

 

[M550344]

The thermal store also has a solar feed which was another reason why I implemented a thermal store rather than going conventional. My Viessmann can accommodate a weather comp but I was advised when the boiler was installed that they were a waste of time.

 

[Worcester]

The problem with the weather comp if its heating the DHW as well as the rads is that the temp of the thermal store may be lowered, so potentially giving a lower temperature / volume of DHW...

 

[Neil K]

So is the solar feed connected up? Or if not have you any plans to connect it up?

 

[Nostrum]

For a minute, to answer the question 'what boiler for the thermal store' you'll need to understand what you expect to take from the store, in order to match a suitable boiler to supply that demand.

So for example, if your property heat losses are similar to that of the boiler output, but you expect to draw off hot water at a rate of 15 litres/min @ 55C, the store will deplete within about 10-15mins (i;e from 80-55)

It could be a number of things, the boiler could not be firing at the appropriate times, the boiler could be undersized, the store could be undersized etc etc

So without the basic design principles you are going to struggle to understand where the fault lies.