Worcester Bosch Greenstar R29 HE - HW but no CH

SidewaysMatt · 27 Sep 2007

Hi, I've had this problem with my system for a few months now and not got to the bottom of it.

Basically I have hot water but no central heating. If I turn the CH on, there's no response at all from the boiler. However the boiler always fires up when the hot water cylinder cools so I've not got a problem with hot water, just no central heating.

I've checked the room thermostat with a meter and that seems to switch OK.

Can anybody give me a few pointers on where to look next?

Cheers

ScottishGasMan · 27 Sep 2007

do you know where your zone valve/s are to operate the ch side of things? good chance if indeed the thermostat is getting power and working ok, the zone valve is not motoring open to let HW into the rads.

SidewaysMatt · 27 Sep 2007

I don't think it's the motorised valve - the boiler just doesn't fire up on demand from the room thermostat. To be honest, I've not checked the thermostat is getting power, I just killed the power and put a continuity tester across the terminals. When the thermostat "clicks on" there is continuity across the terminals, and when it "clicks off" there is no continuity so on that basis I've ruled out the thermostat itself.

SidewaysMatt · 27 Sep 2007

I've had a poke around in the airing cupboard.

Obviously there is the hot water tank (!). I'm guessing the cylinder thermostat is working as the boiler still kicks in to heat up the hot water, so I'm guessing it must be doing that in response to the cylinder themostat.

When the boiler does kick in to heat up the hot water - I can hear the circulating pump (Grundfos 3 speed) running, so I'm guessing that's fine too.

I don't think it's the 3 way motorised valve (Honeywell) as like I say, it's not that the boiler is firing up for the central heating and not giving me hot water at the rads - it just doesn't fire up at all.

I've tried a reset of the programmer (Siemens RWB9 digital). When I switch the central heating from OFF to ON on the programmer, the LCD display dims a bit and the red CH led comes on but there's no response from the boiler.

Could the programmer be knackered? Is it worth bypassing it?

As far as I can tell, there are no fault codes stored on the boiler itself.

Agile · 27 Sep 2007

SidewaysMatt said:
I don't think it's the 3 way motorised valve (Honeywell) as like I say, it's not that the boiler is firing up for the central heating and not giving me hot water at the rads - it just doesn't fire up at all.

You may not think its the valve but we do!

Its a switch in the valve which brings on the boiler! If the valve is not moving then the boiler will not fire up.

Try measuring the resistance of the valve motor! Should be about 2-4 K.

Tony

SidewaysMatt · 27 Sep 2007

Agile said:
SidewaysMatt said:

I don't think it's the 3 way motorised valve (Honeywell) as like I say, it's not that the boiler is firing up for the central heating and not giving me hot water at the rads - it just doesn't fire up at all.

Click to expand...

You may not think its the valve but we do!

Its a switch in the valve which brings on the boiler! If the valve is not moving then the boiler will not fire up.

Try measuring the resistance of the valve motor! Should be about 2-4 K.

Tony

Having done a bit more reading on how these things work (!), I'm inclined to agree with you!

Is it worth just spending £12 on a replacement motor from Screwfix and giving it a go?

http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=102632&ts=84644&id=28670

Agile · 27 Sep 2007

SidewaysMatt said:
Having done a bit more reading on how these things work (!), I'm inclined to agree with you!

Is it worth just spending £12 on a replacement motor from Screwfix and giving it a go?

If you did a lot more reading you would fully agree with me!

But why not just accept that I work on boilers and heating every day?

Best to measure the resistance of the motor and if its o/c replace it?

Tony

SidewaysMatt · 27 Sep 2007

Agile said:
SidewaysMatt said:

Having done a bit more reading on how these things work (!), I'm inclined to agree with you!

Is it worth just spending £12 on a replacement motor from Screwfix and giving it a go?

Click to expand...

If you did a lot more reading you would fully agree with me!

But why not just accept that I work on boilers and heating every day?

Best to measure the resistance of the motor and if its o/c replace it?

Tony

Sorry if that came over the wrong way! No offence meant

When you say measure the resistance, just meter over the two wires from the motor?

SidewaysMatt · 28 Sep 2007

OK, an update. I shoved a meter into the crimp terminals on the end of the leads from the motor and got 2.5K ohms.

I operated the manual lever a few time to check nothign was seized and seemed OK.

When I powered everything back up again I had a play with the programmer. I discovered that if I set HW to ON and CH to OFF, I got hot water. If I set HW to OFF and CH to ON, I got central heating (hurrah!). But if I set them both to ON I only get hot water.

I've done a bit more research - the valve is a Honeywell V4044, with 2 wires (+earth). I'm gessing that means I have a W-Plan system?

I could here the valve operate when I powered up the system. Looking at the wiring diagram and reading stuff on here, is the cylinder thermostat the next likely culprit?

watty11 · 3 May 2009

Hi

I have also had problems with the heating not working but the hot water was ok. I suspected motorised valve so moved arm from auto to manual and locked it into place. Heating will not work without hot water being on so will have to replace valve.

SidewaysMatt · 4 May 2009

This has dug up an old thread!

Just to update this, the fault with my system turned out to be the programmer.

Replaced it with a Horstmann job from Screwfix, and has worked fine ever since

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Worcester Bosch Greenstar R29 HE - HW but no CH

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