System boiler wiring connections.

[jamesBen80]

I've got a traditional central heating system with a 3 port valve, Y plan wiring, room stat, tank stat, and a Bosch Greenstar cdi classic boiler. I've noticed the boiler seems to be running a lot of the time, We've also got a frost stat setup(room and return pipe stat fitting into an outhouse with the boiler) to prevent freezing. I've just popped open the front cover of the boiler and noticed there are lots of connection to the boiler, not just live, neutral and earth, and a switch live. I was always under the impression you linked out the live and switch live on the boiler and let the external controls handle switching the boiler on and off, but with more modern boilers do they need some control of the system components and feed back from the temperature sensors so alter flow and return temps. Does the boiler just measure the return temp and switch off when the returning water gets to hot? or when the external controls say there is no call for heating?

 

[desktop987456]

can't attach links from youtube. search for heatgeek Y plan wiring; there is a series of 4 vidoes on youtube; 3 are for S plan but part 3 is for Y plan. Watch it.

 

[desktop987456]

 

[ianmcd]

I was always under the impression you linked out the live and switch live on the boiler

If you did that the boiler would constantly run with no external control, the switched live is controlled by the mid position valve and the MPV is controlled by the external controls

 

[flameport]

with more modern boilers do they need some control of the system components and feed back from the temperature sensors so alter flow and return temps.

No.
There are no temperature sensors.
Thermostats are just on/off switches. So is the programmer.
It's the same basic on/off controls that have been used for decades.

That boiler can supply power to the rest of the controls, which means 2 extra wires as shown below.
However it's controlled with a single wire, Lr in the diagram.

 

[Madrab]

take a detailed pic of the "lots" of connections you can see in the boiler, As suggested the boiler would normally received a switched live (SL/Lr) from the 3 port valve, the live may be supplied via the boiler as above (may explain the extra wire) or the fused spur, via a wiring centre, depending on how it was wired on install.

 

[jamesBen80]

I've been reading a lot online about boiler modulation and OpenTherm compatible, is that something my Worcester Bosch Greenstar 40CDi classic regular supports? Can't find anything in the manual or online, but it seems to have several spare connection inside the boiler wiring centre?

 

[jamesBen80]

This is how it's wired up currently. To quote a well know Dr "Sorry for the crudity of the drawing I've not had time to do in properly!"

 

[jamesBen80]

Can i get optional controls fitted to my boiler, Like the FW100 of greenstar sense 2, does anyone know if these offer weather and load compensation?

 

[Madrab]

What GS number is it - if it's 41-406-35 then no, I don't believe it supports OT or specifically WB's EMS Bus. Given it doesn't have a E bus then I don't think either of those controls would be compatible but someone with broader knowledge of the older WB's may be able to confirm.

 

[ianmcd]

simple answer is no you cant and it is wired correctly

 

[jamesBen80]

simple answer is no you cant and it is wired correctly

Thanks for that just rung WB and waiting a call back to confirm.

 

[Madrab]

Yup, if anything I'd say there's an extra L (Ls) from the boiler that isn't really needed as the whole system is getting it's live from the FCU but it wouldn't do any harm.

 

[jamesBen80]

Humour me, but to keep the hot water tank at a reasonable temperature say 60C you would need a flow temp of at least 60c if not 65-70C to allow a temperature difference for it to transfer heat to the tank correct? But for my boiler to work efficiently in condensing mode I need the return temperature as low as possible and with a relatively small delta T I can only achieve this by turning my boiler thermostat right down to 2 or 3, at which point the house struggles to get warm and the hot water tank is to cold for showers. I have to keep turning the boiler temperature up and down. Would an automatic control that knows when its heating the hot water and turns the flow temp up as the tank heats up to maximise efficiency when the tank is cold and still allow for a higher more usable final temperature. Likewise the boiler flow temp is kept cooler when the outside temperature is high or the house is cold and the temperature difference between the rads and room temp is high, but if its cold outside and/or as the rads and room temps warm up the boiler can increase flow temperature to provide the required amount of heating and still maximising efficiency? Is this something that all new boilers should be fitted with? My boiler is only 5 years old so this is something my boiler should have come with or be able to upgrade to? According to the boiler info in non condensing mode my boiler is only 88% efficient, not the 97% your sold when looking for a new boiler?

 

[ianmcd]

There are systems that can achieve this , but if you want to have these functions you will need a modern boiler