Strange Worcester Bosch Greenstar Fault

[XrayDave]

Hi,

A bit of a strange one this.

Worcseter Bosch 8000 Life system boiler - installed just under 3 years ago, regularly serviced.

I noticed the flue fan (is that correct) being on when there was no call for heat.

Checked the boiler and sure enough, the temperature display is showing the temp going up.

My house is on 3 floors and split into two zones - each with its own timer/controller & thermostat.

Basement & middle floor on one zone, top floor on a second, separate zone.

So - both timer/controllers OFF (no lights showing) and both thermostats turned right down.

Boiler is showing a flashing radiator symbol and the gas flame symbol. Temp display going up.

Radiators however are COLD (??)

Only way to stop this is to turn the mains power to the boiler OFF.

When either thermostat & controller is calling for heat, the radiators get hot.

Do I need to reset anything (and if so, how) or is there a fault somewhere?

Cheers folks. Over to you.

Oh, no error codes being displayed!

XRD

 

[terryplumb]

Zone valve issue is a possibility, stuck microswitch.
Voltage testing at wiring centre would confirm.

 

[JonathanM]

I’ve had the same problem several times over the years and I've heard it's extremely common. With me, it’s always turned out to be an issue with one of the zone valves.

Apols if you know this already! But the first time it happened to me, I was surprised to be told by the engineer that, (by a slightly convoluted process), it is the zone valves which actually send the demand signal for heat to the boiler. So, if one of the valves is sticking on, the boiler will run even if all the programmers and thermostats are turned off.

I think you should have three zone valves. One for each zone and one for the hot water cylinder. Being hopeless at electrics, I wasn’t able to do the electrical tests on the valves. But each time I had the problem, it was easy for me to diagnose which valve was causing the problem, simply by feeling which pipes were getting hot.

 

[XrayDave]

Thanks for the replies guys.

Yes, I think I knew that the Zone Valves actually call for heat but had forgoten!

I think I have 2 Zone valves - one to direct flow through the heating coli for the DHW tank and the other to direct heat through the top floor rads.

I have a (partially) working system - but I have to fiddle.

What is REALLY confusing is that the boiler is saying LoPr 0.7 bar, I put a very small amount of water in and it goes to 1.3 bar. I drain a bit off - literally a bit to get it to 1.0 bar - and the boiler fires up and the rads get hot - then it yells that it is over pressure 'STOP' and displays 1.4 bar.

WTF is going on??

Currently boiler saying it is heating water (gas flame icon is lit on the display and I can hear the bellows of the gas meter sighing) and the temperature display is going up but the radiators are cold - including the flow and return pipes.

XRD.

 

[ianmcd]

you either have a sticking end switch on one of your zone valves but you will need a multimeter to confirm, or your cables connecting everything are too close, worcester are the worst for EMF false switching but they sell a resistor that gets fitted to the boiler that stops this

 

[XrayDave]

Thanks Ian

The wiring hasn't altered in the last 3 years (the WB boiler was installed in May 2020) so I think the emf "problem" is unlikely. The boiler was working fine until I noticed the pump running almost continuously yesterday afternoon and investigated.

The zone valve end switch seems more likely. One zone valve is ancient - must be at least 26 years old, possibly more. That said, the old stuff tended to be built to last rather than the newer stuff which seems to be designed with a shorter working life in mind.

Heating engineer calling Monday evening so I'll know more by then.

Dave

 

[ianmcd]

Thanks Ian

The wiring hasn't altered in the last 3 years (the WB boiler was installed in May 2020) so I think the emf "problem" is unlikely. The boiler was working fine until I noticed the pump running almost continuously yesterday afternoon and investigated.

The zone valve end switch seems more likely. One zone valve is ancient - must be at least 26 years old, possibly more. That said, the old stuff tended to be built to last rather than the newer stuff which seems to be designed with a shorter working life in mind.

Heating engineer calling Monday evening so I'll know more by then.

Dave

yep agree it is most likely to be an end switch sticking, very common

 

[XrayDave]

Okay - so some further info to aid diagnosis of the problem ...

We have a system boiler with a hot water tank. DHW setting on the boiler is 60C.

The hot water has been OFF since at least Saturday evening / first thing Sunday morning. Even then only for, like, 10 mins at a time to 'top up'.

The grandchildren had a hot bath (not too deep) on Saturday night. This usually means the hot water is warm rather than hot.

The hot water, more than 24hrs after being 'ON' is still too hot to keep your hand under.

We have been 'manually' turning the heating on and off using the 240V supply to the programmer. When OFF, this turns the boiler completely OFF as the timer/programmer and thermostats seem to be having no effect on the call for heat.

The boiler setting for the radiators is 65C.

This morning, when I went to look at the boiler with the heating ON, it was showing 70C

So, three questions.

(1) Is the very hot hot water (when OFF) indicitive that a zone valve is stuck open - allowing hot water to circulate through the DHW tank when the heating os on?

(2) Would a 'stuck open' zone valve be calling for heat when the timer/programmer and thermostat(s) aren't?

(3) Why would the boiler be showing a CH temp of 70C when it is set to a maximum of 65C? Is this normal or unusual?

I'll run some hot water & stick a thermometer in it to see what the temperature is coming out of the tap (should have done this before penning this response) and update this post/thread.

UPDATE: 54C coming out of the tap.

Pictures of the zone valves

DHW Zone Valve (the one that I think may be the problem)

Upstairs (Zone 2) - which seems to be working as expected (i.e. turning the heating to that zone on and off) under the control of the programmer/timer and thermostat for that zone.

Thanks in advance,

Dave

 

[JonathanM]

We have a system boiler with a hot water tank. DHW setting on the boiler is 60C.

It sounds like you can set the DHW temperature on the boiler separately to the CH temperature?

According to the manual excerpt below [6] this can only happen if you have had the optional integral diverter valve fitted. Do you know if this is the case?

 

[XrayDave]

It sounds like you can set the DHW temperature on the boiler separately to the CH temperature?

According to the manual excerpt below [6] this can only happen if you have had the optional integral diverter valve fitted. Do you know if this is the case?

View attachment 295011

Hi Jonathan,

I don't know for sure but we must have. We can set the DHW temperature differently to the GCH flow temperature.

During the long hot summer of 2021 we had the heating off from around March to October and only the hot water coming on twice a day for like 10 mins at a time. When we put the heating back on, the radiators wouldn't warm up and seemed to need constant bleeding and the boiler was yelling about low pressure almost constantly (see this thread if interested). Turns out it was a build up of hydrogen (?) due to corrosion during the long lay-off.

As the hot water got hot, I guess we must have the diverter valve but I couldn't say for sure.

Dave

 

[XrayDave]

Hi Jonathan,

I don't know for sure but we must have. We can set the DHW temperature differently to the GCH flow temperature.

During the long hot summer of 2021 we had the heating off from around March to October and only the hot water coming on twice a day for like 10 mins at a time. When we put the heating back on, the radiators wouldn't warm up and seemed to need constant bleeding and the boiler was yelling about low pressure almost constantly (see this thread if interested). Turns out it was a build up of hydrogen (?) due to corrosion during the long lay-off.

As the hot water got hot, I guess we must have the diverter valve but I couldn't say for sure.

Dave

Duplicate post - don't know why!

 

[JonathanM]

I don't know for sure but we must have. We can set the DHW temperature differently to the GCH flow temperature.

It doesn't look like you have got the diverter valve kit fitted from looking at your previous photo below. AFAIK those two blank holes in between the shiny brass fittings would be fitted with extra valves like in the image below yours. Just to check we're talking about the same thing, are you saying you can press the tap symbol on the boiler control panel and set the hot water temperature in your hot water cylinder? Do you also have a thermostat on the cylinder itself?

 

[XrayDave]

It doesn't look like you have got the diverter valve kit fitted from looking at your previous photo below. AFAIK those two blank holes in between the shiny brass fittings would be fitted with extra valves like in the image below yours. Just to check we're talking about the same thing, are you saying you can press the tap symbol on the boiler control panel and set the hot water temperature in your hot water cylinder? Do you also have a thermostat on the cylinder itself?

Hi Jonathan,

Yes to both questions.

Pressing the Radiator key (number 7 in your earlier post) we can set the CH temperature - currently set to 65C and pressing the Tap key (number 8 ), we can set the DHW temperature - currently set to 60C. Yes we have a cylinder stat clamped to the side of the cylinder beneath the insulation.

DHW set to 60C

Rads set to 65C

Implicit in your reply is that the boiler doesn't have a diverter kit and that it should have - i.e. it hasn't been installed correctly? Am I understanding that correctly or does the presence of a cylinder stat negat the need for a diverter kit?

Information Triangle (top line) indicates an error? How do I access the error code?

Dave

 

[XrayDave]

Another duplicate post!!!!

Why am I getting two posts of the same thing all of a sudden?

 

[JonathanM]

Implicit in your reply is that the boiler doesn't have a diverter kit and that it should have - i.e. it hasn't been installed correctly? Am I understanding that correctly or does the presence of a cylinder stat negat the need for a diverter kit?

It was just information gathering, trying to work out how your system was set up, in case that shed light on your problem. But it's only confused things I would imagine! I wasn't suggesting it hasn't been installed correctly. You don't need the diverter kit for the boiler to work properly. The diverter kit just allows the boiler to be set up to work in a different way. Is your engineer still coming this evening? Is it the same engineer who did the install?