No Hot Water - Unvented System

[Shadoman]

Hi All,
I have a strange problem that started 2 days ago. I have a Worcester Bosch Boiler and Unvented Cylinder. Been working solid for 3 years. Yesterday, there was no hot water at any outlet (tap/showers). It was just lukewarm.
The thermostat was set to call for hot water but the boiler wasnt firing. I noticed that the pipe from boiler to Cylinder was lukewarm.
I switched on heating and the boiler fired up and heating was fine at the rads.
This also led to the pipe going to cylinder to heat up (hot to touch). But the Hot water outlet at the cylinder remained lukewarm.
This didnt make sense as the coil pipe was hot but water leaving the cylinder was lukewarm.

I did some research and someone mentioned trying to reset the cylinder stat and this didnt work. I pushed the power button to power cycle the boiler and still the boiler didnt fire for hot water.

But then I switched of the power to the wiring centre for the boiler as well as the boiler. And on switching it on the boiler fired and we had hot water.

Today, we had the same problem. Hot water ran out and I had to switch off power to the wiring centre and the hot water came back.

I see the wiring centre supplies the cylinder stat and and the valves so Im assuming something is wrong there and resetting the power is temporarily forcing one of those to reset.

Any advice on what is going on here would be greatly appreciated. I have contacted my installer but currently not had a response.

Thanks

 

[terryplumb]

Motorised valve issue probably. Show some pics of the valves . The motorised valve sends voltage to the boiler to fire up ,if cylinder stat is calling for heat .

 

[Shadoman]

Thanks. Here are some pics.

https://drive.google.com/drive/folders/1zsgVppGd0HVbNNzwOEy6oSlsEihU6DCt?usp=sharing

 

[ianmcd]

if you want the best help just upload your pics on this site, you just go to the bottom right of the page and click on upload a file

 

[Shadoman]

Thanks, didnt see that.

 

[ianmcd]

OK test the DHW zone valve, with no demand for HW the lever on the side should be able to be slid across, but with some resistance, then with a demand for HW the same lever shouldnt have any resistance when you slide it across

 

[Shadoman]

Thanks. So I tried this and it worked as you described. But in this case, when I called for the hot water, the boiler fired up as expected so its working anyway.
Should I repeat the test when the water has gone call, the hot water is being called and the boiler is not firing? Or is that a pointless test?

 

[terryplumb]

Bit difficult to diagnose what's wrong ,when all is working ok. Intermittent faults can be a PITA !! Next time hot water doesn't come on ,re do the test.

 

[Shadoman]

Thanks, will do. Quick question though. If the valve is faulty, I don't understand why when the central heating was on, the pipe for the hot water coil to the cylinder, just after the valve was hot, but the water leaving the cylinder was lukewarm. That confused me totally, as if the coil is getting hot, why wouldn't the water in the cylinder be hot and therefore leave the cylinder hot. The egress pipe on the top of the cylinder was lukewarm in this case. Am in missing something?

 

[terryplumb]

Yes ,the coil has two pipes ,one in ,and one out ,both on the side of the cylinder.if one is hot and the other not ,there is no flow through the coil ,and you won't get your water heated. The pipe at the top is the distribution pipe to taps / showers ,no hot water in tank and distribution pipe wont be hot .

 

[Shadoman]

Thanks, that makes sense. I'm away from home tonight but will check this tomorrow.

 

[Shadoman]

Thanks to both of you for replying. Yes, it is the valve. Is this something I could replace myself or should I get someone in to do it?

 

[terryplumb]

If your confident enough ,have the tools ( to support the valve body,and undo the nuts ,you need 2 spanners ,or one plus a large pair of grips),and know what to do ,you can.

 

[dilalio]

Valve or actuator?
Take head off.
Manipulate and lubricate spindle.
Change head.

 

[Shadoman]

Thanks Terry. Do I need to change the whole valve? How would I know? I'm guessing it's just the actuator.
I've seen a lot of people say "replace the head" what does that mean exactly? Is that just replacing the motor, or does it mean replacing the whole metal not that sits above the valve.
Sorry to ask the basic questions.