Linking Combi Boiler to Solar System

[learningallthetime]

We have a hot water solar heating system which is connected to a vented hot water cylinder.

Rather than keep using the expensive immersion heater I would like to combine the Worcester Bosch 24i combi boiler we have for our central heating with the cylinder.

The Glenhill solar cylinder has a spare indirect coil (22mm). So the idea we are thinking about is:

Zone the central heating system into 2 zones, 1 for normal central heating and a separate zone to connect to the spare indirect coil.

For this I think I will need the following:

1) 2 zone, 7 day programmer - Honeywell
2) 2, 2 port zones - Honeywell
3) A wiring centre - Honeywell 2 port
4) A cylinder thermostat - Honeywell

Use the existing Samsung wireless room thermostat and receiver.

The questions I have are:

1) Should the zone ports by normally open or normally closed?
2) Does the system need a bypass valve? If so, where does this get installed.
3) Is a 2 core, 0.75mm heat resistant flex ok to run from the cylinder thermostat to the wiring centre
4) To extend the cable on the zone valves, do I need 5 core heat resistant flex (plus an earth cable).
5) Do you rewire the zone valve or connect the extra length of cable to the original zone valve cable via some sort of junction box.
6) Do I need any additional plumbing to be introduced? E.g. one way check valve or isolation valves?
7) The cylinder has a 22mm male connector on the spare coil. Do you feed a short length of 22mm pipe with an olive on it and tighten with compression nut?
 
Is the following wiring diagram ok?

http://wiki.diyfaq.org.uk/index.php?title=File:S-Plan-Wiring.gif

Thanks in advance for any help.

[Iain]

Hi
Set mine up as
http://www.navitron.org.uk/forum/index.php/topic,1572.msg10940.html#msg10940
so sounds similar
You will probably need an electronic tank stat as the hysteresis on a mechanical one is too great. I use a Carel digital stat with a .5 deg hysteresis and works well.
Iain

[learningallthetime]

Hi Iain,

Where you state you have converted your combi boiler to a system boiler, did you do a similar thing to what I was thinking i.e. run the cylinder zone as part of the central heating overall loop.

This would mean the central heating side of the boiler has 2 zones, 1 zone that goes to the radiators and the other to the cylinder. The hotwater part of the programmer would be unused as this was for instant hot water in the combi set-up.

I note you have more than the 2 zone valves I was planning, so I was trying to get my head around where are systems are the same and where they differ?

Thanks for your help.

Rob

[micko]

My system is similar apart form a mains cylinder. The zone valves are closed unless the hot water or central heating calls for heat and the one ore both valves are powered open. Turn the hot water off on your combi and just use the central heating side you have to leave the heating side on all the time on the boiler and controller everything from the separate heating/ hot water controller and room stat. in addition to the live feed to the boiler you need a live from the wiring centre, terminal 10 I think down to your boiler, this has to be connected to the boiler in order to fire it up.

I did not use a Honeywell control. I used a Horstmann. The reason is I did not want my hot water coming on at a set time, if you have solar heat hopefully this will give you most of your demand.  The Horstmann has a one hour boost function so if the solar heat is a bit low I just use the boost for an hour rather then the timer.

Ignore the pump in the diagram.The live in the diagram at the boiler is a switched live, you need an additional permanent live to keep the boiler on.

You do not need heat resistant flex to extend the zone valves. I would just joint them rather than trying to replace them. I have never taken a zone valve apart so whatever is easiest.You can get a ten way box, you could run both zone valves into on of these and extend from there. 

It may be a 22m X ¾ bsp fitting on your cylinder. You can get these at any plumbers

No bypass valve in mine, ask Worcester Bosh via their website..  

[Iain]

Hi Rob
Yes, I have 2 zone valves. 1 for the CH and one for the HW
2 channel programmer. CH timed as normal.
HW I have to come on in the morning at 0600-0700 for the morning showers. Will only heat if the chlinder is below 44 deg C. So only tops up the solar. If I need hot water in the evening I only need the 1 Hr boost if not enough solar. My cylinder temp thermostst is set to 45 degC so the boiler only heats the cylinder if below this.and the sensor is about 1/4 way down the cylinder so the boiler only heats the top of the cylinder
My other Zone valve is only used to enable the heat dump circuit.

The combi part is still there but has a stop valve on the outlet. If everrything fails I can just isolate the cylinder(1 valve) and open the valve on the combi.
Iain

[learningallthetime]

Hi again,

I've taken a look at the connectors on the Worcester Bosch 24i Junior boiler and I have the following options for electrical connections on the main board:

L
N
NS
LS
LR
Earth Block

Am I right in thinking that in the wiring plan: http://wiki.diyfaq.org.uk/index.php?title=File:S-Plan-Wiring.gif

It will wire up as follows:

L connected to the live on terminal block 1 which gets live from the mains supply
N connected to the neutral on terminal block 2 which is connected to the mains supply
Earth connected to the earth on terminal block 3 which is earthed at the main supply
LR - return live from terminal block 10 (call signal from the valves)

This would leave NS and LS unused

Is this bit correct?

Thanks again for all your help
Rob

[greentangerine]

My take on retaining the combi was to heat the thermal store with an evacauted tube array and (at this time of year) a wood burner and have the output from the TMV on the store and the DHW on the combi valve operated and controlled by a stat on the store.  If the store is hot enough, the valve on that is open and the one on the combi closed and vice versa. 

So basically I get the benefits of both; been working like this for nearly two years now flawlessly.  The valves take about a minute to cycle between open and closed states so there's an overlap when it occurs which is barely noticeable if you are having a shower at the time; usually the store is being switched out and the combi firing up.

I did investigate feeding the store output to the combi input via a blending valve etc but one of the major reasons I didn't do that was the physical distance between them and how I'd run the 22mm copper across the entire house.  I wasn't too convinced by the savings in gas by doing so either; I'd estimate 90%+ of our hot water comes from the store over the year.

[micko]

yes you are correct.

When its time to do it you need the live neutral and earth as you say feeding the boiler . Just take a link from the boiler live to Lr or Ls and see which one fires the boiler up, after that connect  this boiler terminal up to 10. The two way valve gets a call to open from the controller, it then moves and puts a live onto 10 (orange) this in turn fires your boiler up.



Don’t forget everything has to come off the same circuit