Which controller for a 37CDI ?

[Isleman]

I will be putting a new central heating system and already got three quotes .
While all installers agree the Worcester 37CDI is a good choice for my setup ( a three bed 1960 semi) they don't seem to agree on the controllers.
One is proposing a Drayton Digistat + RF room thermostat
http://www.screwfix.com/p/drayton-digistat-rf-room-thermostat/73146#
Another one is the Honeywell CM927 and the last one the WORCESTER DT10RF DIGISTAT MK11
So my question obviously is which one should I choose ?
Which are the pros and cons ?
I assume with the Worcester controller there are no compatibility issues while I understood from another post on this forums that CM927 can't control preheating the hot water and radiators in the same time.

 

[D_Hailsham]

All installers agree the Worcester 37CDI is a good choice for my setup (a three bed 1960 semi).

May be OK for the hot water (did they check the flow rate and dynamic pressure?), but it's massively oversized for heating with a CH output of 9.4 -30kW, particularly if your house has been insulated and had cavity windows fitted.

Use the Whole House Boiler Size Calculator to find your Heating Requirement. Set the Domestic Hot Water Allowance to 0kW as you want a combi boiler.

The Heating Requirement should be within the boiler CH range (9.4 -30kW) and preferably well above the minimum. If it isn't the boiler will spend much of its time cycling on and off and you may have difficulties getting the house up to temperature.

As for controllers, The Honeywell CM927 is a programmable Central Heating only thermostat and the Drayton Digistat+ RF is just a CH thermostat, so neither is suitable.

The Honeywell Sundial RF2 Pack 2 would be suitable.

 

[Isleman]

May be OK for the hot water (did they check the flow rate and dynamic pressure?), but it's massively oversized for heating with a CH output of 9.4 -30kW, particularly if your house has been insulated and had cavity windows fitted.

The Honeywell Sundial RF2 Pack 2 would be suitable.

I have checked using the calculator and the result was 4.7KW with cavity and loft insulation over 75 mm and 10.3 without any insulation.
I will have my insulation done next month so obviously I will need only 4.7 kw.
The reason they over sized it is that I mentioned a possible extension being built in 2-3 years and running on the same boiler.
As for the controller I found it here
http://www.plumbnation.co.uk/site/h...-programmer---thermostat-pack-2--y9420h1008-/

Thank you very much for the tips .

 

[mickyg]

isnt that a 2 channel programmer? why would you have that for a combi??
Why not get one of WB own stats like an FR10, gives you room modulation control, much better

 

[D_Hailsham]

I have checked using the calculator and the result was 4.7KW with cavity and loft insulation over 75 mm and 10.3 without any insulation.
I will have my insulation done next month so obviously I will need only 4.7 kw.
The reason they over sized it is that I mentioned a possible extension being built in 2-3 years and running on the same boiler.

But even if the extension doubles the size of the house, you will only need 9.4KW, which is the lowest the boiler will modulate down to. So it's still massively oversized.

What is the incoming flow rate and dynamic pressure? If you don't know ask the installer to check it.

If you propose adding an extension, how many bathrooms and shower rooms will you end up with? If more than one, a combi boiler may not be the best solution.

 

[Isleman]

But even if the extension doubles the size of the house, you will only need 9.4KW, which is the lowest the boiler will modulate down to. So it's still massively oversized.

What is the incoming flow rate and dynamic pressure? If you don't know ask the installer to check it.

If you propose adding an extension, how many bathrooms and shower rooms will you end up with? If more than one, a combi boiler may not be the best solution.

I think you point is valid and after reading more about the subject it seems that indeed the 37 CDi is massively over sized for my needs
I was looking at the 30SI or even 25 si but is still modulating only from 7.2 KW which is still more than what I need.
I think would be nice to find something to modulate from 3 KW up to 24 Kw unfortunately Worcester is not having a combi boiler to offer this range.

I will check with the plumbers to see what pressure they got when they done their testing.

On the extension I will have just one extra bath which will include a shower. However I don't think I will have two bathrooms running on showers at the same time.