Worcester Bosch greenstar 18ri heating problem

[warehouseman]

Fairly new condensing boiler Greenstar 18ri (with hot water tank). Away from house for a week. Left the C/H switch at 'ON' with the wired thermostat in hall at 15c. The H/W left 'off' . On return, house was very cold - less than 9c. Increased thermo in hall to 25c , waited & nothing happened. Checked that the settings were ok. Then as a last resort, i slightly moved the thermostat on the boiler 5mm clockwise & it came on !!. Problem solved I thought. after testing a few times satisfactorily, put hall thermostat back to 15c.
Came back 7 hours later and same thing had happened. Cold house. At some point it had failed to click in again.
As before, I increased the thermo on the boiler clockwise ---but this time, nothing happened at all. Eventually, while leaving the C/H switch at 'on' , I also turned the Water onto 'on'. This started the water heating but also got the central heating to start, as I noticed the radiators warming up.
Any ideas what the problem is ? Cant work out if it is the boiler, the setting controls panel (potterten) or the hall thermostat (which you can hear the clicking when you increase). Has happened a couple of times again in the last few days.
Any help appreciated before I call someone out .

 

[payney1974]

would normally come up with an error code but just check your condense pipe from the boiler isnt frozen outside.

 

[warehouseman]

Do not think its the pipe, payney, as this is fitted to the plumbing inside the house.

 

[payney1974]

do your rads get hot if you have your hw on but ch turned off? (As long as your cylinder stat is calling for heat)

 

[warehouseman]

No, the radiators do not heat up if H/W is only one 'on'. Its just that when we are unable to get C/H to start, we have to turn the H/W on as well. Once the boiler starts, we can then turn off the water & the heating continues !

 

[payney1974]

Thats a strange one! i can only think the three way may be playing up. Cant be 100 % though.

 

[doitmyself]

It's just that when we are unable to get C/H to start, we have to turn the H/W on as well. Once the boiler starts, we can then turn off the water & the heating continues !

The HW can be OFF for two reasons: turned OFF at programmer, or turned ON at programmer but water has reached temperature, so cylinder thermostat opens.

Can you check that you are unable to get CH only in both conditions. You can mimic the second by turning HW ON at programmer and turning cylinder stat to minimum.

 

[warehouseman]

Sorry, but i think u misunderstand doitmyself. If u read my first note, i was away for 7 days. The H/W was off. Therefore water was totally cold. Heating was programmed to come on at 15c ---- and never came on. The latter situation of reaching the water temperature has not occurred. Water heats fine anyway when needed.
It is the fact that some time during the C/H 'on' situation when the heating is working (and when the H/W is off), the boiler obviously stops at some point but never then re-starts when the temp drops below 15c