Central Heating won't come on, but boiler works OK

[pphilpot]

Hi all

I hope that this is a simple problem. I just tried to turn my central heating on this morning, but the boiler doesn't fire up when the timer is advanced.

The boiler fires up for hot water heating OK, and the 3-way valve seems to work when the CH timer is advanced to 'on' - I can hear the whir of the 3-way valve moving and if both water and CH are set to 'on' then I feel warm water reaching the radiators. The room thermostat is clicking OK.

The red light on the timer comes on when CH is advanced to 'on', but the boiler isn't fed any mains (i.e. the 'Mains on' light on the boiler isn't lit).

I've tried to check the room thermostat with a digital multimeter and while I'm not quite sure what I'm testing for, the Live (1) to Neutral (3) changes value when the dial is turned and clicked...

Here's the gear:

Boiler: Worcester Danesmoor 15/19
Timer: Drayton LP241
Room thermostat: Honeywell T40 (basic dial type)

Many thanks for any suggestions of what to look for.

Cheers

Paul

 

[seco services]

if heating/hw come on when both are called for then i wouldn't suspect the wall stat.
if boiler don't come on when only heating called for i would suspect the 3 port valve.

heating only should have power on the white wire and orange wire.
if only power on the white then the valve is not activating the micro switch or the micro switch is liable to be faulty in the valve.

 

[D_Hailsham]

heating only should have power on the white wire and orange wire.
if only power on the white then the valve is not activating the micro switch or the micro switch is liable to be faulty in the valve.

I think you mean grey.

 

[pphilpot]

Hi both

I'm not really sure what I'm doing But...

Grey | White
HW X 0
CH X X
CH+HW X X


X denotes power. Is the above correct?

 

[D_Hailsham]

Grey | White
HW X 0
CH X X
CH+HW X X

X denotes power. Is the above correct?

No!

It should be:

Grey | White
HW 0 0
CH X X
CH+HW 0 X

 

[seco services]

heating only should have power on the white wire and orange wire.
if only power on the white then the valve is not activating the micro switch or the micro switch is liable to be faulty in the valve.

I think you mean grey.

yes as D_Hailsham pointed out white/grey.
orange live to boiler/pump.

 

[pphilpot]

Grey | White
HW X 0
CH X X
CH+HW X X

X denotes power. Is the above correct?

No!

It should be:

Grey | White
HW 0 0
CH X X
CH+HW 0 X

OK, I'm using the blue as neutral i.e. where the blue wire goes into the connection strip. This also reads as live on the grey wire even when neither HW or CH is on.

BTW, this did all work as it should last spring, and the HW has been working as it should all summer.

Just a guess here. Could the 3-way valve be sticking

 

[seco services]

This also reads as live on the grey wire even when neither HW or CH is on.

the grey will be live when heating/hw off as the grey is live from the programmer hw off terminal.

 

[pphilpot]

This also reads as live on the grey wire even when neither HW or CH is on.

the grey will be live when heating/hw off as the grey is live from the programmer hw off terminal.

Thanks Seco - at least that part seems to be correct

 

[seco services]

what make/model is the valve ?

 

[pphilpot]

what make/model is the valve ?

The valve is an old Honeywell "Sundial Y plan 3 position Diverter Valve" - there's no apparent model number on it though.

I have a spare one that came with a second hand pump a while ago which is an iflow "Mid Position Actuator" model MA 1. Is this interchangeable with the above should I need to change it?

Many thanks for your time so far!

 

[seco services]

you can take the top lid off and check it's making the micro switches when on call for heating only.
heating called for only should be live on grey, white and orange which is call to boiler/pump.
yes you can change it for a MA1.

 

[pphilpot]

you can take the top lid off and check it's making the micro switches when on call for heating only.
heating called for only should be live on grey, white and orange which is call to boiler/pump.
yes you can change it for a MA1.

Right - problem isolated. Great tips/advice seco services!

The motor isn't moving far enough to push the micro switch - and it sounds weaker than maybe it used to (I can't really remember). If I manually close the micro switch the boiler fires up.

Do I make the assumption that the mechanical valve is stuck/gunked up? If so I guess fitting this MA1 may be my easiest option...

Many thanks again

Paul

 

[seco services]

Do I make the assumption that the mechanical valve is stuck/gunked up? If so I guess fitting this MA1 may be my easiest option...

yes can be the valve it's getting stiff etc.
sometimes putting the valve in its relaxed position hw port open heating closed.
you can do this by either calling for hw so the boiler fires or isolating the fused spur and turning it straight back on.

and put a screwdriver on the part that the spring is connected to and pushing the valve fully open a few times, sometimes it frees the valve enough so it then hits the m/switch when heating called for.
may only be where it's not be in that position all summer.

if fails change to the MA1.

 

[pphilpot]

put a screwdriver on the part that the spring is connected to and pushing the valve fully open a few times, sometimes it frees the valve enough so it then hits the m/switch when heating called for.
may only be where it's not be in that position all summer.

Problem solved! Perfect, thank you very much.