Y Plan not working

[Pengwyn]

Hi,
I got a phone from my father in law last night.

His central heating isnt working ! It is a back boiler set up, Y plan I think.

Nothing fires up the boiler, although the pilot is lit.

Any tips on where to start would be great guys, thanks.

Alan

 

[gas4you]

Check the 3 port valve head if everything else is calling for heat.

Sounds like the microswitch has broken in it.

 

[namsag]

Check the fuse and that no isolating switches beside boiler have not been turned off accidentally

 

[Pengwyn]

Check the fuse and that no isolating switches beside boiler have not been turned off accidentally

Defo not that.

"Check the 3 port valve head if everything else is calling for heat.

Sounds like the microswitch has broken in it."

If the 3 port valve was broken wouldn't the boiler still fire up ?

 

[gas4you]

No. It is the valve head that tells the boiler to fire up.

 

[Pengwyn]

Thanks gas4u.

Is there a wiring diagram I could look through to get it clear in my head, ie what initiates the signal to the boiler to light, micro switiches etc, valve position.

 

[gas4you]

Look HERE

You may have to register first, then you can view the 'Y' plan circuit diagram.

 

[MANDATE]

No. It is the valve head that tells the boiler to fire up.

True for CH only but not for HW. Pengwyn said 'nothing fires up the boiler'.
With HW only there is no power going to valve. Without power valve returns to HW only position ( return spring). Power does go from HW ON terminal of programmer to 'com' terminal of cylinder stat and across stat to satisfied terminal and then to boiler.
This will go via the 10 terminal junction box and I would think the problem is somewhere along this route.
It needs to be checked at the cylinder stat for 230volts input and output.
This will indicate if the problem is further back (terminal box or programmer) or further ahead (boiler connection, gas valve or neutral wire connection).

 

[Pengwyn]

Mandate.

That is a great description.

I check this out tomorrow and get back.

Alan

 

[cider]

Or just listen for the pump running, boiler and pump both run off the same feed from diverter valve

If the pump is running its prob the gas valve gone

 

[MANDATE]

Or just listen for the pump running, boiler and pump both run off the same feed from diverter valve

If the pump is running its prob the gas valve gone

When HW only is ON the boiler and pump are fed from the cylinder stat.
It is when CH only is ON, the valve triggers micro switch No 2, this allows power out through the 'orange' wire to join up with that from cylinder stat.
So HW only, power from cylinder stat.
HW and CH, power from cylinder stat.
CH only, power from valves 'orange' wire.

 

[cider]

Yes, but putting it into laymans terms (this is a DIY site) generally on any heating fault on a fully pumped system if the boiler is not running but the pump is, its a boiler fault. If the pump and boiler are both dead its a controll fault.
Thats the first thing I always check and you dont even need to open your tool box.

 

[namsag]

With cider on that do the basics first

 

[stevies62]

Check for 240 at the gas valve. If you've got that, your gas valve has gone.

 

[Pengwyn]

Thanks alot guys.

From your descriptions I managed to get it down to the Danfoss HS3 valve. The micro switch connected to the orange wire has burnt out.

Thanks for your help.


Where is best to buy one, the valve itself is ok, just the actuator assembly needs replacing.