Hot water but central heating only works in the mornings .

[emin-j]

Hi all, this evening the central heating has not come on although we have hot water, the timer seems to be ok with red light on but combi does not fire up when timer is changed from auto to on ,I think the problem is with the boiler.
The boiler is a Vaillant VCW 240H and is quite a few years old (bit like me)
I have had a quick look at the boiler but wont get much of a chance until the weekend to have a go at it.
When the hot water tap is turned on there is a definite 'click' should I be looking at the diverter valve next ?
Does the pump operate for DHW of just heating ?

thank you.

 

[twgas]

These are pretty complicated boilers, there are many reasons why the CH might not work.
External controls first.

 

[emin-j]

The heating came on this morning but not this evening - strange.

 

[twgas]

Does the servo valve...

(its on top of the water section) move when you run a hot tap, then go back when tap is turned off.

 

[emin-j]

Thank's twgas, I will have a look Saturday.

 

[emin-j]

Does the servo valve...

(its on top of the water section) move when you run a hot tap, then go back when tap is turned off.

Hi twgas, yes the servo valve works fine also checked the diverter valve which moves when hot water tap is turned on.
Heating has now come on for the last three mornings and works fine but does not work on the evening setting or the 1hr on or on/all day setting could it be a timer problem ? the red light shows on the timer when set to heating but the boiler doesn't fire up the timer is a Danfoss 103e7

 

[twgas]

Sounds like it could be the timer, can you check it's sending power out at the times it should be on but isn't working?

 

[emin-j]

Sounds like it could be the timer, can you check it's sending power out at the times it should be on but isn't working?

Cant quite understand how the timer works as the cable from the timer to the boiler seems to be a permanent live ?
The cable from the timer goes into a frost stat then into the panel below the on/off switches where I tested for power which was showing live although at the time the heating was in the off position on the timer, but does this 'live' need to be there for the dhw to work ?
As the heating works perfect in the mornings I cant see there can be a fault with the boiler shall I just change the timer ? I can pickup the Danfoss 103 which is the mechanical version of the 103e7 for under £30.

 

[emin-j]

Have now fitted a new timer and there is no change
I set the timer to constant and the pump was running but the boiler did not fire up, I turned off the pump by the switch on the boiler panel then turned it back on again, the pump started then there was a click and the boiler fired up the heating ran for around five minutes then the gas flames gradually died out then the pump stopped and I couldn't get the heating to come on again or the pump to run I turned the hot tap on and the boiler fired up and heated the water no problem, where do I look next

 

[twgas]

Does the diverter move to the left when the heating is turned on

 

[emin-j]

Does the diverter move to the left when the heating is turned on

Hi twgas, I will check the diverter for c/h just strange that the heating comes on and runs perfect in the morning (7.30am) but wont fire up in the evening could it be a temperature sensor which allows the boiler to fire up in the colder morning temperatures ?
DHW is working fine.

 

[twgas]

To be honest, i would have to suspect the programmer, but to have 2 with the same fault is pretty unlikely.
Try linking out the external controls, connections 3&4 (I think)

 

[emin-j]

Heating came on tonight ! strange.

 

[bellairaphon]

What is your room stat set to?

Nath

 

[emin-j]

What is your room stat set to?

Nath

Hi, we don't have a room stat only the 1-10 selector on the boiler currently set to number 4 , boiler has been working fine the last few days, strange.