Hot water but no heat from WB Greenstar 28i Junior

[ShivUK]

Hello all. I've been poking around similar looking threads but I wanted to get some more thoughts about what's going on.

I have a Grenstar 28i Junior combi boiler that started acting up today.

When there is demand for central heating, the boiler will end up in a fault state - based on the combination of flashing lights I end up with and the repeated sequence of firing up then shutting down along the way, it seems this is an ignition lock out state - as per the service manual.

When there's only a demand for hot water, however, everything is fine.

If I press and hold the service button for 10 seconds and then release then my central heating will kick in and my radiators will heat up nicely - this lasts for about 10 or 15 minutes and the boiler shuts down again.

The manual suggests checking the following in the ignition lockout state:

Gas present and at correct pressure.
Combustion CO2 level.
Flue condition.
Ignition electrodes / harness / connections.
Gas valve (coils 140-190Ω) / low voltage harness connection. Otherwise replace control board.

But looking at previous similar posts on this forum, there's a suggestion that it could be something to do with the diverter?

The sequence diagrams in the manual suggest that if there was a problem with the diverter being in the wrong position that the boiler shouldn't even spin up the fan or try to ignite.

So what do you think the cause is likely to be?

Also, in terms of getting somebody out to repair, how much do you think it would cost? I'm trying to weigh up calling somebody out for this job vs getting on to british gas an their £109 + £25/month option.

Any thoughts or advice would be greatly appreciated!

 

[ianmcd]

sounds more like an external control fault, timer or room thermostat fault

 

[ShivUK]

sounds more like an external control fault, timer or room thermostat fault

Thanks for the reply and the suggestion!

I'm 99% sure it's not the thermostat; it's a pretty simple one that simply closes or opens a circuit and I've verified that the resistance across the device drops to zero when it should be calling for heat. I've not gone as far as simply closing the circuit across the two wires, but I might try that and see if I still have the same problem. I expect that I will.

EDIT; I've also forced the boiler to be in the "on" position in order to bypass the timer.

EDIT Again; I've read up some more about the service mode; it enables hot water and central heating; does this lend any credence to the idea that the diverter is the problem?

Hot water - fine
Hot water and heating - fine
Heating alone - not fine

 

[CBW]

EDIT; I've also forced the boiler to be in the "on" position in order to bypass the timer.

Service mode is for engineers when analysing the boiler

 

[ianmcd]

The service mode over rides all controls for about 10-15 mins, hence why I think you have an external control fault

 

[martyndc88]

There'll be an issue with your combustion. minimum has probably drifted out, or possibly a part has started to tear. A good service should sort this out. I'd probably avoid British gas at the Moment, they're having issues with engineers at the moment.

 

[ShivUK]

After leaving the thermostat off all night, I went and turned it up again this morning and the heating came on fine; stayed that way for an hour or so but eventually ended up with the fault again. Was able to do this again after another couple of hours idle.

At least we aren’t freezing cold!

I put out some messages to a few people yesterday to see if anybody can come and have a look. No replies yet... Easter weekend not the best time for problems, I guess.

 

[martyndc88]

Worcester fixed price repair might be an option for you

 

[ShivUK]

Worcester fixed price repair might be an option for you

I'll look into what they offer. Thanks for the tip!

 

[Stadan20]

Yea possibly combustion problem on low rate . Put boiler into service mode then turn left hand dial all the way down . Does boiler stay lit ?

 

[ShivUK]

Yea possibly combustion problem on low rate . Put boiler into service mode then turn left hand dial all the way down . Does boiler stay lit ?

I'll try this tomorrow morning. Can't be messing about too much after my daughter's bed time.

As it happens, the whole system has been performing just fine since around lunch time today. ‍

 

[ShivUK]

Yea possibly combustion problem on low rate . Put boiler into service mode then turn left hand dial all the way down . Does boiler stay lit ?

Just had a go at this.

In service mode with the left dial all the way down (i.e. at 1, not the frost protection setting) it goes round in the same ignition/off loop that I'm seeing when it's trying to operate normally - it stays lit for a few seconds and then shuts down and immediately fires up again. When I bump it up to max heat in service mode then it stays lit the whole time.

I'm going to try leaving the boiler on max and see if it helps in the short term.

Still no reply from the folks I reached out to.... so I'm glad there's some way to get heat into the house!

 

[Stadan20]

Yeah sounds like combustion issue to me spect the gas valve just needs tweeking . If the boiler has never had a full strip service you would probably benefit from having that done also

 

[ianmcd]

call worcester bosch and get them to service it, at least it will be done properly, and they will carry any parts required

 

[ShivUK]

I finally managed to get somebody out to have a look today. They took one listen to the boiler and said "condensate's blocked" - they opened up the boiler and sure enough there was a load of gunk in the condensate trap.

Cleaned it out and put it back in and things seem much better already. Will need to see if it makes it through a full 24 hours without problems before I start celebrating.