Boiler does not turn on for hot water

robshak

[Deleted User] said:

Forgive me if this has been mentioned before. The OSO RI series of unvented cylinders have a built in cylinder thermostat. It sits behind the screwed metal plate. It might be worth TURNING THE HOUSE POWER OFF; unscrewing the plate to see if the thermostat needs to be reset.

If that doesn’t work, then any remedial work undertaken on an unvented cylinder must be carried out by a G3 annotated Gas Safe engineer. Unvented cylinders have three levels of thermal safety built into them to prevent any possibility of explosion.

https://youtu.be/61uDmQF5I2E?si=Dxa3qyE9n-yiMhck

Ha ha ha..that's insane, why would one want to have that bomb in the house..glad ours is in the loft..no worries, no plans to do ANYTHING at all..just trying to educate myself a bit for when the the Gas Engineer comes to sort this out...all covers closed and shut now and organising an visit by a competent professional :-)

Was just curious as to why it failed when all was working fine until we went on holidays.

Also, tried RESET a while ago, to no effect. Thanks anyway!

FreeBear

robshak said: Phew!! That test pen was a God send!!

Just be aware that those non-contact pens can give false positive readings, and very occasionally false negatives. Never rely on them being accurate, and always confirm with a proper multimeter set to AC Volts (at least 400V).

Those screwdrivers with a neon in the end are even worse. Cheap ones, and ones that have been stored in damp conditions have the potential to give you a nasty shock (or even kill). And they are even worse for giving false negative readings.

Milltir

robshak said:

FreeBear said:

QrizB said:

Qyburn said:

The five core black sheath are the valves.
Are we sure this is a combi boiler?

It's definitely a combi boiler, but it's being used as a system boiler.
This seems to be confusing a few people.

If you look at the last picture of the boiler internals, there appears to be just three pipes going out of the bottom. One gas, one flow, and one return. I'm fairly sure it is a system (heat only) boiler (Greenstar 30CDi ?). No DHW heat exchanger visible either.

Spot on FreeBear, it is a Greenstar 30CDi..a few more photos to demystify things a bit..

Last photo - 1 is vent, 2 is gas, 3 is outlet, 4 I think is inlet because it is connected to tap you add in water to increase pressure.

I also ran a live feed check with programmer on for DHW on and my findings are:

- Cable P, assuming from programmer passes live feed to HW tank, I followed cable, hence cylinder thermostat has live feed.

- Boiler white core brown cable takes live feed from pink wires from silver boxes black cores. This is dead.

- Sliver boxes take live feed through grey cables connected to live brown from 1. This is live.

- It seems current disappears once it goes into silver boxes via grey cables but doesn't come out via pink cables to pass it to the Boiler. 

- Also 5/S is dead.

Phew!! That test pen was a God send!!

Doesn't the nameplate label "Classic System" indicate this is a system boiler, not a combi boiler?

Reed_Richards

If all else fails...

This is from the manual for the Greenstar 30 CDi System boiler



So that hot water control knob is still there but for use only with an "optional diverter valve".

Qyburn

robshak said:

I also ran a live feed check with programmer on for DHW on and my findings are:

- Cable P, assuming from programmer passes live feed to HW tank, I followed cable, hence cylinder thermostat has live feed.

- Boiler white core brown cable takes live feed from pink wires from silver boxes black cores. This is dead.

- Sliver boxes take live feed through grey cables connected to live brown from 1. This is live.

- It seems current disappears once it goes into silver boxes via grey cables but doesn't come out via pink cables to pass it to the Boiler. 

Silver boxes are the valve actuators, one for CH and one for HW. This is a wiring diagram for a typical install. For each valve there's a pair of wires, Brown and Blue in the diagram, when these are live (from the programmer) the valve should open. When open, the other two wires Grey and Orange are connected by the internal switch to fire boiler and pump.

Have you checked whether the HW valve moves when the programmer's calling for HW?

Or if you can open it manually, and if does then do you get flow to the cylinder?

Tracing power, when calling for HW the following should be live, check in this order to see where it's going wrong ..
1. HW On output from controller to cylinder thermostat
2. Return from thermostat
3. Live to valve motor (Brown)
4. Switched live from valve Orange

robshak

Qyburn said:

robshak said:

I also ran a live feed check with programmer on for DHW on and my findings are:

- Cable P, assuming from programmer passes live feed to HW tank, I followed cable, hence cylinder thermostat has live feed.

- Boiler white core brown cable takes live feed from pink wires from silver boxes black cores. This is dead.

- Sliver boxes take live feed through grey cables connected to live brown from 1. This is live.

- It seems current disappears once it goes into silver boxes via grey cables but doesn't come out via pink cables to pass it to the Boiler. 

Silver boxes are the valve actuators, one for CH and one for HW. This is a wiring diagram for a typical install. For each valve there's a pair of wires, Brown and Blue in the diagram, when these are live (from the programmer) the valve should open. When open, the other two wires Grey and Orange are connected by the internal switch to fire boiler and pump.

Have you checked whether the HW valve moves when the programmer's calling for HW?

Or if you can open it manually, and if does then do you get flow to the cylinder?

Tracing power, when calling for HW the following should be live, check in this order to see where it's going wrong ..
1. HW On output from controller to cylinder thermostat
2. Return from thermostat
3. Live to valve motor (Brown)
4. Switched live from valve Orange

"Have you checked whether the HW valve moves when the programmer's calling for HW?" - No. 
" Or if you can open it manually, and if does then do you get flow to the cylinder?" - Yes.

If I just call for HW in the programmer, the boiler does not come on.  If I call for both CH and DHW, the boiler turns on and sends hot water to radiators but still not towards the hot water tank.  If I manually open the valve in the actuator towards the tank, the hot water DOES flow through the hot water tank thereby heating water inside it. At this time, all cables are live.

HOWEVER, as soon as I switch off the CH in the programmer with only DHW called for, the boiler shuts down.  Then:

Tracing power, when calling for HW the following should be live, check in this order to see where it's going wrong ..
1. HW On output from controller to cylinder thermostat - Live
2. Return from thermostat - Live
3. Live to valve motor (Brown) - Live at junction box (cannot check in actuator box as no open connection)
4. Switched live from valve Orange - Dead

So it clearly is pointing out that live feed is disappearing into the actuator valve box is not being sent out via orange cable to the boiler.

Even when manually opening the valve in the actuator, there is still no power to the boiler.

Does this mean we have narrowed the issue down to this valve?  Was it meant to send live feed via orange wire to the boiler connection when hot water was called for?   Thanks.

FreeBear

It is possible the contacts in the micro-switch inside the valve head have burnt out. The switches are not normally a replaceable item, so you have to buy a new head.

robshak

Nailed the !!!!!!.  The reason boiler doesn't turn on is because the little flap that moves when valve opens and pushes the micro switch in the actuator DOES NOT touch the switch. Looks like it is not going fully back, even when valve is opened manually.  When I pressed the switch with the tester, voila, the boiler turned on!!!!!

Shame I cannot enclose a video.

So does this mean a new valve head will resolve this mystery?

I also assume when the HW is called in the programmer and live feed gets to the valve, it opens then pushing the micro switch turning the boiler, like magic!!!  I have learnt a LOT and I don't want to stop :-) Thanks to you ALL!!!

deano2099

Glad you sorted it! We have a similar set up and narrowed it down the same couple of things (tank thermostat or valve) - during winter, the boiler wouldn't kick in to heat the tank. We figured "well at least there's a backup immersion heater, will turn that on so we have some hot water" and after about 15 minutes, the boiler fired up and started heating it. We realised running the immersion heater would somehow trigger the boiler. We were going to get it sorted but since we've not had the heating on, it's worked flawlessly without needing to do this.
Thought it must be the tank thermostat but now wonder if it's a similar thing to you but the temperature is causing the microswitch to expand/contract...

robshak

deano2099 said:

Glad you sorted it! We have a similar set up and narrowed it down the same couple of things (tank thermostat or valve) - during winter, the boiler wouldn't kick in to heat the tank. We figured "well at least there's a backup immersion heater, will turn that on so we have some hot water" and after about 15 minutes, the boiler fired up and started heating it. We realised running the immersion heater would somehow trigger the boiler. We were going to get it sorted but since we've not had the heating on, it's worked flawlessly without needing to do this.
Thought it must be the tank thermostat but now wonder if it's a similar thing to you but the temperature is causing the microswitch to expand/contract...

I stayed away from turning the immersion heater on so far because it costs a fortune!!!! Ha ha

I have tried it though, to troubleshoot, the water I the tank gets hot but does not trigger the boiler on..the last three years we have been here, it has worked fine without having to rely on immersion heater..no plan to change it 😀