Greenstar 35CDI Problem

[Doug99]

Hi Guys,
My boiler isn't firing up when CH demanding heat by the room thermostat.
Symptoms are:
When demanding heat - green flame light illuminates and fan runs up.
After about 20 secs the fan slowly runs down to a stop and the green flame light goes out.
The boiler is now all quiet as the temp gauge quickly rises to 90 then slowly cools to around 50 after few minutes .
I am assuming the gauge is monitoring water temp in the boiler as the pump isn't running.
I switch off/on the mains to the boiler and it carries out its normal 15min re-cycle, after which the boiler heats up my radiators as it should.

But when the demand for heat is off overnight, the CH does not kick in again in the morning, and have to repeat the on/off sequence.
Very frustrating as there are no error codes showing any time.
All radiators have been vented and system pressure is at the normal 1bar.
The boiler is serviced annually.
Any thoughts?
Cheers All

 

[CBW]

Sounds like the diverter stepper motor/paddle (assuming combi version) is getting stuck, or not energising across to CH.

 

[kidgreen61]

As CBW says, it sounds like the DV motor may have died, which does happen on these boilers.
You can see if its working by removing the green rubber cover and observing the motor when calling for heat/HW.
You can also operate the paddle with your finger having pulled the motor out first, if the boiler works fine with the paddle held in CH position, then you've found the problem, 5 min job to replace motor.

 

[Doug99]

Thanks guys - but if the diverter motor is defective, why does the CH work after each on/off recycle sequence?

 

[CBW]

Thanks guys - but if the diverter motor is defective, why does the CH work after each on/off recycle sequence?

Like I said, it could be getting stuck, or the voltage could be sporadic

 

[Doug99]

Symptoms changed - CH not firing up at all now even after an on/off cycle - Boiler detects demand for heat then flashes between symbol -11- and water temp. Haven't touched anything yet as the missus in no rush as weather is warming up.

 

[CBW]

If the symbol looks like x2 letter T’s placed on their sides, then this is the siphon fill mode and will stay in this for 15 minutes and nothing will override it.

 

[Doug99]

Hi Guys, the diverter valve and motor have been changed and I've been advised that the system needs a flush.
It hasn't been flushed since the boiler was installed 12yrs ago so it is well overdue.
My rads are all connected via 10mm pipework and it appears that a normal chemical flush would not be sufficient.
Is the power flush preferred for such a system and what is the difference in process?
Cheers All
Doug

 

[Madrab]

It hasn't been flushed since the boiler was installed 12yrs ago so it is well overdue.

if the system was clean then it wouldn't need a flush, there isn't really such a thing as an overdue flush IMO, if you see what I mean. It only needs flushed if the system is dirty and the rads need cleaned out. Is the system water really dirty/black? If it was serviced properly every year though, then it shouldn't have ever got to the point of needing a power flush, is it a large company suggesting a power flush?

It will need a cleaner introduced and run for a while to loosen/dissolve the crud. A chemical flush (sometimes called a mains/gravity flush system type dependent) would use a cleaner and then the system drained/filled/flushed/drained/filled/flushed ...... etc till it runs clear. A power flush uses a pump/filters and mechanical action to force the system clean, even then though a chemical would usually be used, prior to the work, to make the whole process easier and more effective.

A flush is always difficult with a 10mm microbore system. To be effective each rad would need connected to flushed individually as the 10mm pipework is too restrictive to allow a centralised flush. AlternativelyEach rad could be removed and manually flushed outside with a hose.

The boiler is another matter if the HEX(s) are blocked up.

 

[Doug99]

Thanks Madrab, the local independant plumber did suggest that an individual rad flush would be the most effective due to the 10mm system. A couple of downstairs rads do have cool areas which suggest sludge is present. When draining a couple of litres from my downstairs bleed valve......it is black
By HEX....do you mean heat exchanger? Can that be cleaned of sludge easily enough?
Cheers

 

[Madrab]

Yup, cleaner in for a week or 2 then drain system, rads off the wall and hose in and flush back and forth. e.g flush from one end till clear then the other end, up end it and fill it right up then drain, keep doing that back and forth till clear. It will go clear then if you swap ends you'll be surprised how much more gunge there is. If the rads have easily removeable bleed valves and end caps then get them off too and flush it back and forth through each opening, rubber mallet on rad and tap to loosen any stubborn crud.

Can I presume it is a sealed system with 22mm pipework to the boiler? If so then with cleaner in and flushing that through using the filling loop. Then open every rad valve when it's rad is off the wall and ensure the pipework flushes clean through and pressure is the same at every valve to check there are no restrictions.

 

[Doug99]

It is a sealed combi system with 22m pipework to the boiler. A flush of the rads it is then.........I had better check i have enough PTFE tape

 

[Doug99]

The system is all up and running again, however I have noticed that what I assume is the fan, is permanently running. With DHW and CW not being demanded the fan is running with a very slight vibration I can hear downstairs when everything is quiet. Before my problems discussed previously it was a quiet runner.
Looking at the installation manual, the fan should only run up on demand.
The 'Eco' button is illuminated so I am not pre-heating the DHW.
I've tried the reset and on/off trick but no change.
Any thoughts?
Cheers
Doug

EDIT - I've just switched on CH from cold and there is a definite run up of the fan so it must be the pump continuously running. The engineer replaced the pump so could the new one be inadvertently wired differently to permanently run?

 

[Doug99]

It seems that the new water pump is of a different wiring set up, so when fitting to an older boiler it causes the pump to run continuously.
New pumps now require a compatible new PCB which is now on order. A sly move by Worcester Bosch. Fortunately all being cover by my boiler insurance.

 

[gazfen]

Your premium will be doubling lol