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JamesI, Developer
Category: HVAC
Satisfied Customers: 5759
Experience:  I have a portfolio of renovated houses, including DIY projects from installing bathrooms and new heating systems to rewiring.
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I have an old Worcester oil fired boiler which has served us

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JA: Hi. How can I help?
Customer: I have an old Worcester oil fired boiler which has served us well for many years. The CH is not switching on, however the hot water is. I have changed batteries in the thermostat a Honeywell cm901. I have looked at the wiring of the ppump and 2 way valve (?) - no damage.
JA: Are you getting any error codes or blinking lights on your boiler?
Customer: No errors to rest. It just does not come on. Its fine when I trigger the HW
JA: How long has this been going on with your boiler? What have you tried so far?
Customer: See above ....
JA: Anything else we should know to help you best?
Customer: no - this happened out of the blue.

Hi, thank you for choosing Just Answer, my name is ***** ***** I will help with your query today.

Do the CM901 is showing demand for heat, but the boiler not seeing a demand?

Customer: replied 7 months ago.
that is right. The CM901 looks ok, & I changed the batteries
Customer: replied 7 months ago.
I saw the phone suggestion, lets just chat
Customer: replied 7 months ago.
Hello ?
Customer: replied 7 months ago.
I am going now. I just tried putting the 2 way valve open on manual and putting both CH and HW on at the timer. I did not feel any heat coming to the rads but may not have given enough time. I suspect the control device on the burner. Its a Sartronic 830.3 which is solenoid and mechanical switch type. I look forward to your solution.

You can ignore offers for calls these are just adverts for optional services.

I would check the thermostat alot of the time the relay has failed in them, so check the demand for heat is closed circuit, if it is that rules out the thermostat.

Let me know how you get on

Customer: replied 6 months ago.
James, I took the thermostat off and tested it with a multi meter.It is definitely switching when I adjust the temperature setting. Only2 wires connected - very basic. I also checked the wiring to a junction box leading to the valve and pump. Everything looked ok. The valve moved manually and the pump worked when it was triggered by a call for HW .

Ok and does the thermostat terminate at the boiler or on the valve actuator?

Customer: replied 6 months ago.
The single wire from the thermostat goes to a junction box with connections/wires leading to both the motorised valve and the pump. There is a wire going away also.

Ok so you need to determine how this is wired up, normally you would have the pump being controlled by the boiler, and the demand for heating into the boiler going via the value actuator.

So check your getting power to the actuator and if there is demand but the actuator not opening.

Customer: replied 6 months ago.
Please bear with me, this is a bungalow with a pressurised system and all the valves, pumps are in the loft under insulation and the wiring is complicated by lighting etc - lots of grey wires. I may be wrong about where the stat wiring goes as it s behind panels (I am sure this only has 2 wires (fawn & grey)+ earth. The 2 big cables coming into the box one has 3 brown wires (some sleeved) and the other has the normal, blue brown green/yellow. I checked the pump wiring - its ok; the valve wiring is ok. There is a jumper to the pump on the brown wire.
I found online a diagram which I think fits what I am seeing The C plan.
My motorised value only has 5 wires no white).
With the system switched to CH - timer on and room thermostat on, there is no voltage across any of the wires at the box or pump. Maybe there is another box ?
I am also confused by the boiler which has only one set of wires in - standard 3 core. No obvious control wires.

The C Plan is a traditional setup, so what you need to establish is with a demand from the stat are you getting a voltage at pump or valve.

If not then you need to go back to the timer and stat and make sure they are outputting demand.

With regard to the boiler whats the model of boiler and I can tell you where the call for heat line comes in.

Customer: replied 6 months ago.
OK, I'll check the stat and programmer. for power. The boiler is a Worcester Danesmoor 15/19 possibly pre 2005 model (HPJ 19000) but the manuals for the 2005 model from internet match.

Looking at the installation manual here, page 17 shows the configuration you should have.

Customer: replied 6 months ago.
James - do you mean the config inside the boiler ? I have not looked there yet except to inspect the thermostats as that manual says they could be an issue. I'll see if there is anything loose

Yes inside the boiler, as I say something is causing a open circuit (lack of demand) so you need to follow the circuits and bypass components until you find the cause.

Customer: replied 6 months ago.
James, I could not see anything amiss but I would add that my wiring does nor replicate that exactly. Bearing in mind that the HW fires up perfectly, I'll focus on the CH wiring. If the thermostats were an issue, should I short them with a wire ? (but again if HW works then it might not be them).
I got a new sartronic and switched out the old one but that but it made no difference.

You need to be careful about shorting (make sure you short the correct terminals), but thats what I would do so you know you have a constant CH demand and can then go back to the valve actuator, pump and boiler to see what is at fault.

Customer: replied 6 months ago.
James, good morning. When I was checking over the boiler, it was clear there was no power coming in, There are 2 sets of wires coming into the switch for the boiler. I assume these are from the CH valve/stat and the HW valve/stat. The brown on one is giving power, the other wires are red / blue - zero power - so I guess thats the fault, and is the CH valve/ pump. This latter is directly wired to the boiler, the first is only picking up the neutral, the brown is isolated.
Checking the motorised valve, the output line is the orange and I can see some power there but not 220v.
The room thermostat has power and switches.
The timer has power and switches - only thing is a yellow wire is for CH on and I can see no yellow wire downstream (maybe there is a fuse somewhere?).
If you agree that possible a wire break is where the fault is then its not an easy fix and I need to call someone in.
Customer: replied 6 months ago.
Sorry if I dont make sense - its difficult to edit the text is you write a lot. I repeat
2 sets of wires to the switch
one set giving full power, the other none, and this is the one powering the boiler.

The circuit would be fused but normally at the boiler end, but as your getting power at the thermostat I dont think its the fuse.

So yes I would be inclined to agree you have a cable break, as you have checked each component (pump, valve, programmer and stat) and they all appear to be functioning.

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