Boiler Replacement

[Terry lambert]

The 12.7 ltr min. Quoted by the manufacture is at a 35 degree temperature rise which is how manufactures state their flow rates. Which is too cool for normal use.

Not true.

As the hot water is not being stored, there is no need to heat it to 60C to kill off any legionella bacteria which might be present in the water, so the water only needs to be heated to the safe working temperature, which is 41C for a shower and basin and 44C for a bath. Since cold water rarely falls below 10C, and may be as much as 20C, a rise of 35C is more than sufficient. If you heat the water to 60C using a combi, you then have to mix it with cold water to bring it back to a safe temperature. This wastes energy.

If you set your combi to 35 degrees for hot water to get the 12.7 Ltrs a min
you would have a complaining customer on your hands, this was raised in the cc

The 831 has a flow restrictor for a 42 delta t at 10 ltrs a min

 

[Razor900]

The Atmos also has much better flueing options which can be useful when replacing a powermax

 

[Luis21x]

Would I gain much by installing a Vaillant 837 instead of the 831 model. We have a 2 bed semi-detached with one bathroom.

Or is that just unnecessary overkill ?

 

[mickyg]

its not really about whats suitable its more a case of what your used to. I have customers with a 24kw combi for a 5bed 2bathroom house and they're fine with it, equally Ive got customers with a 1bed apartment and 1shower and they think a 28kw is inadequate.

 

[Terry lambert]

Would I gain much by installing a Vaillant 837 instead of the 831 model. We have a 2 bed semi-detached with one bathroom.

Or is that just unnecessary overkill ?

As long as you have the adequate incoming flow and pressure theirs no problem going upto an 837

The boiler itself isn't physically much bigger, the 37 kw is on the hot water and the boiler will auto range rate to suite the system on the heating side ( new version)

So if you have the incoming supply the only downsides to the 837 over the 831 would be that it's a little bit more expensive and slightly bigger.

 

[D_Hailsham]

If you set your combi to 35 degrees for hot water to get the 12.7 Ltrs a min you would have a complaining customer on your hands, this was raised in the cc

The 831 has a flow restrictor for a 42 delta t at 10 ltrs a min

I think you are confusing the actual temperature with the temperature rise.

The figures quoted in manufacturers' specs are the temperature rise. So a DeltaT of 35C means that it will increase the temperature of the water by 35C, i.e from 5C to 40C or from 20C to 55C.

In contrast to that, the hot water temperature dial on the boiler sets the actual output temperature, so if it is set to 35C, the water will come out of the tap at 35C - provided the incoming temperature is not too low and the flow not too fast..

I am not suggesting that an output temperature of 35C is sufficient, just that a rise of 35C would be as it will provide a flow of between 40 and 44C, which is the recommended safe temperature for baths etc.

Heating the water to a higher temperature than actually required is a pointless exercise.

 

[Terry lambert]

I understand delta t. If I havnt articulated that properly, I appologise.

The fact of the matter in this case is that although the boiler lists a delta t of 35 with a flow rate of 12.7

This boiler has a restrictor for a 42 delta t at 10 ltrs min

I understand what your saying about raising the temp and then having to blend to reduce it. If a 35delta t was enough the manufactures would not fit restrictors to a 42 delta t

Worcester etc do the same

I would love to be able to tell customers that their boilers when commissioned will give them the flow rates listed but that's not the case

Don't take my word for it, as an engineer you can phone tech of any of the Manu your self and they will tell you this

 

[Terry lambert]

If you set your combi to 35 degrees for hot water to get the 12.7 Ltrs a min you would have a complaining customer on your hands, this was raised in the cc

What I meant above, is the manufacture setting the delta t to 35 instead of 42 not the temp control nob. I can see why that was not clear.

I do not set the parameters the manufacture does.

 

[Dan Robinson]

If my bath was only 44 degrees I would be mightily pished off.

 

[D_Hailsham]

The fact of the matter in this case is that although the boiler lists a delta t of 35 with a flow rate of 12.7, this boiler has a restrictor for a 42 delta t at 10 ltrs min

Now I understand what you were on about.

I remember reading somewhere that a new regulation was coming out restricting the flow rates from showers to 10 litres/min. If you combine that with the recommended safe temperatures of 40C to 44C, you can see why manufacturers are putting restrictors in their boilers.

After all a boiler which can deliver 12.7 lpm at 35C can also deliver 10.58 lpm at 42C or 10 lpm at 44.45C.

 

[D_Hailsham]

If my bath was only 44 degrees I would be mightily pished off.

You obviously do not have a TMV on your bath!

It doesn't apply to normal households, but the Health and Safety Executive can take action against organizations responsible for children and vulnerable people if there is a risk they can get into a bath with a water temperature above 44C.

Third degree burns can be caused by:

One-second exposure to 70°C water;
Half-minute exposure to 55°C water;
Ten minute exposure to 50°C water.

 

[Luis21x]

Hi All,
I'm considering a Potterton Titanium 40kw unit which delivers 16 l/min flow rate for £1600 suppled and installed, with a 5 year warranty. I think they are a recently released boiler.

What are your thoughts on these boilers ?


Regards,

 

[Dan Robinson]

Actually I have this bad boy:

http://www.altecnic.co.uk/index.php?option=com_k2&view=item&task=download&id=365

Set to around 47 or 48.... Lobster hot .

 

[mickyg]

Hi All,
I'm considering a Potterton Titanium 40kw unit which delivers 16 l/min flow rate for £1600 suppled and installed, with a 5 year warranty. I think they are a recently released boiler.

What are your thoughts on these boilers ?


Regards,

I wouldnt buy any new products from the baxi group going on their last release. Have you measured your hot flow yet??

 

[Terry lambert]

I'm not a baxi fan either

Based on gas wizards calcs a 40 kw boiler should give you 13.6 ltrs min at a delta t of 42

Contact baxi and find out if this is the actual flow rate you will get from this boiler.

And as Mick said test your existing