Boiler Coming On Unprompted

[BenH1989]

Hi all,

Boiler: Worcester Greenstar 28i Junior

Been having some issues with the boiler coming on unprompted. It has no thermostat hooked up so I know it’s not that. It works off a timer which it seems to just ignore. I unhooked and disconnected the timer front panel and it still came on unprompted and intermittently. So I’m fairly certain it’s not a dodgy timer as it seemed to be unaffected.

I looked in the manual to find if it’s a freeze stat and there isn’t one connected. I suppose because it’s located in the kitchen.

I then got a multimeter and saw that there was a live signal to LS & LR and I don’t know where from. It could be a permanent signal or not as it’s not on all the time but most of the time. Running out of ideas of what it could be and hoping the nice people of diynot could offer some advice?

Thanks in advance. Ben

 

[CBW]

Hi Ben,

If you’ve no room thermostat connected, then you will get live between the 2 LS and LR as they’ll be connected by a link wire. You’re saying it’s coming on, do you mean firing up intermittently, is it heating the radiator circuit, do you have a preheat on that model?

 

[ericmark]

From what I remember that is a combi boiler with an Eco button, with Eco on the boiler should only work when there is a demand for domestic hot water or central heating, with Eco off it heats a small tank inside the boiler so the water is instant, this means the boiler will fire up every so often.

It seems the boiler changed over time, later models can have a special Bosch thermostat with modulates the boiler with connection to ebus, early models can only use return hot water to control output.

The theory was the boiler pumps hot water around the system, if all TRV's are open then the water is cooled so the return water is cold or cool so boiler runs flat out, as the TRV's close the return water has a smaller and smaller route and finally it will open by-pass valve so the return water gets hotter and hotter which causes the boiler to modulate (turn down flame height) and then cycle off/on.

So in theory it does not need a thermostat fitting. However in practice it will continue cycling on/off all summer, so normally a thermostat is fitted so as summer arrives it will turn off.

So in your case it would seem it's the heating of the domestic hot water causing it to fire up, try pressing Eco button that should stop it. I found Eco set on the taps can be cracked open to give a trickle of hot water, Eco off and taps must be wide open for boiler to fire up, Eco on resulted is shower getting warm then cold then warm again as boiler tank ran out, eco off once warm stayed warm.

 

[ianmcd]

you say live to LS &LR is there a link or are there seperate wires going into there, if seperate wires what are they connected to ?

 

[BenH1989]

Hi Ben,

If you’ve no room thermostat connected, then you will get live between the 2 LS and LR as they’ll be connected by a link wire. You’re saying it’s coming on, do you mean firing up intermittently, is it heating the radiator circuit, do you have a preheat on that model?

Yes. It is firing up intermittently with no obvious demand and heating up the radiator circuit yes.

From what I remember that is a combi boiler with an Eco button, with Eco on the boiler should only work when there is a demand for domestic hot water or central heating, with Eco off it heats a small tank inside the boiler so the water is instant, this means the boiler will fire up every so often.

It seems the boiler changed over time, later models can have a special Bosch thermostat with modulates the boiler with connection to ebus, early models can only use return hot water to control output.

The theory was the boiler pumps hot water around the system, if all TRV's are open then the water is cooled so the return water is cold or cool so boiler runs flat out, as the TRV's close the return water has a smaller and smaller route and finally it will open by-pass valve so the return water gets hotter and hotter which causes the boiler to modulate (turn down flame height) and then cycle off/on.

So in theory it does not need a thermostat fitting. However in practice it will continue cycling on/off all summer, so normally a thermostat is fitted so as summer arrives it will turn off.

So in your case it would seem it's the heating of the domestic hot water causing it to fire up, try pressing Eco button that should stop it. I found Eco set on the taps can be cracked open to give a trickle of hot water, Eco off and taps must be wide open for boiler to fire up, Eco on resulted is shower getting warm then cold then warm again as boiler tank ran out, eco off once warm stayed warm.

Hi ericmark, I think you may be onto something. Yes it does have an eco button. It's a new property so still learning about the boiler. As you say I put it into eco and it was much more responsive for obvious demand, i.e. turned on and off with the on and off switches. However, it seems to totally ignore the timer. It will not fire when the timer says to fire and with the switch obviously on the timer setting. This is quite inconvenient as it means constantly turning it on and off unless we leave it out of eco.

you say live to LS &LR is there a link or are there seperate wires going into there, if seperate wires what are they connected to ?

Good question Ian. Let me have a look and get back to you on this one.

 

[CBW]

So you say there’s no room thermostat, but heating the radiators, I’d be looking towards the diverter motor or valve assembly.

 

[ericmark]

Unless fault with boiler radiators should not get hot with a domestic hot water demand, so seems some thing wrong.

The boiler unless time clock built into boiler should has two line supplies, one for domestic hot water and to allow cool down, and one when central heating required from time clock.

In this house on moving in found one of the three and earth cables open circuit so DHW and CH had been combined, I could not have DHW without CH.

There is a long list of faults with mine, some I just could not believe the last owners lived with, however they were there.

My cure was to fit Nest but that is unlikely to help with your boiler.

 

[CBW]

Hi Ben,

You said a new property, is this a new build property or just new to you?

 

[BenH1989]

So you say there’s no room thermostat, but heating the radiators, I’d be looking towards the diverter motor or valve assembly.

Yes when the boiler wasn't on eco it would heat up the radiators unprompted. Switching to eco has seemed to solve this intermittent problem and it is purely on or off now with the switch on the timer. However, the boiler doesn't ignite when on timer mode. Purely, on or off.

Unless fault with boiler radiators should not get hot with a domestic hot water demand, so seems some thing wrong.

The boiler unless time clock built into boiler should has two line supplies, one for domestic hot water and to allow cool down, and one when central heating required from time clock.

In this house on moving in found one of the three and earth cables open circuit so DHW and CH had been combined, I could not have DHW without CH.

There is a long list of faults with mine, some I just could not believe the last owners lived with, however they were there.

My cure was to fit Nest but that is unlikely to help with your boiler.

Do you think Nest would solve it when in Eco mode? As I said to The Novice's post, the eco seems to have solved the boiler firing unprompted. It just seems the timer doesn't work now.

Hi Ben,

You said a new property, is this a new build property or just new to you?

Apologies. Yes it's a new property to me. It's a 1935 house. I estimate the boiler about 12 years old. The boiler is also losing pressure and a bit of fault finding on Sunday led me to believe it's the expansion vessel. When pressing the nipple only a tiny puff of air came out. I've pumped it back up to 1 bar, see how we get on.

 

[ianmcd]

I've pumped it back up to 1 bar, see how we get on

did you leave a drain point open when pumping the vessel up ?

 

[BenH1989]

did you leave a drain point open when pumping the vessel up ?

All pressure was out of the system.

 

[ianmcd]

All pressure was out of the system.

So you didnt open a drain point then ? then you havent done it properly, read the FAQs on how to do it properly, what you have done wont work

 

[dilalio]

All pressure was out of the system.

Not the same as open to atmosphere!

 

[BenH1989]

So you didnt open a drain point then ? then you havent done it properly, read the FAQs on how to do it properly, what you have done wont work

Ah okay I’ll have a look at the FAQs. Thanks for prodding me in the right direction.

Any thoughts on the timer aspect of the boiler being unresponsive?

 

[ianmcd]

I looked in the manual to find if it’s a freeze stat and there isn’t one connected. I suppose because it’s located in the kitchen.

That is only additional frost protection, your boiler still has internal frost protection and it could be that is faulty, when you say you disconnected the timer, which timer and how did you disconnect it ?