Worcester 20 25 heat slave

[Gary65]

boiler works fine for rads and hot water, but after reaching required temp and shutting off a noise continues .. sounds like a fan or air blower. Sometimes stops in minutes other times hours. sometimes doesn't happen at all

 

[SimonG]

Could have a post purge board fitted. Once the burner has finished burning the post purge will run the burner motor to empty the combustion chamber of combustion gases to prevent fumes being pushed back into the property.

 

[SJB060685]

Post purge most likely, assuming the noise is localised to boiler? What burner is it?

I believe post purge is wired through a PCB in control panel on this boiler.

 

[Gary65]

HI both, thanks for the input. It is a Worcester Heatslave 20 /25 and I have taken the lid off and checked that it does have a post purge PCB - which is then connected to the main board

I have found a new post purge board to purchase from a decent supplier - just wondering whether swapping the board is something I can attempt as a DIY job.

 

[SJB060685]

HI both, thanks for the input. It is a Worcester Heatslave 20 /25 and I have taken the lid off and checked that it does have a post purge PCB - which is then connected to the main board

I have found a new post purge board to purchase from a decent supplier - just wondering whether swapping the board is something I can attempt as a DIY job.

The purge unit should only have a couple strips with wires going to it and fix in place. It should be a simple job providing electrical supply is isolated first. If you're sure you have the right part number and have found the correct replacement you could give it a go, if you don't feel confident then please get an engineer out. Bare in mind there is a couple variations of the post purge units for the heatslave over the years so make sure it is the right part.
I have spoke to my associates with more experience on this unit than myself and most of them agree that these units are more hassle than they're worth and the other option is to link the unit out. I'm not going to say how to do that but it is an option and experienced engineer can undertake it for you should you wish.

 

[Gary65]

Thanks again for the clarification. I did think about bypassing the fan but prefer to keep it in use since the boiler has been fine with it for many years.
The part number seems accurate - so I will attempt the swap out of the board let you know how I get on

 

[SJB060685]

Thanks again for the clarification. I did think about bypassing the fan but prefer to keep it in use since the boiler has been fine with it for many years.
The part number seems accurate - so I will attempt the swap out of the board let you know how I get on

I might be misinterpreting what you're saying but the fan is an important part of the combustion process, pre purge and post purge, plus if the motor and fan weren't energised you'd have no ignition. It should not be linked out all together! Linking the post purge out just stops the fan continuing after the stats have shut the control box and burner down. Your problem is the timed relay on the post purge board, it should run after burner shutdown for a set period of time, yours is acting randomly.
Swap the unit over if you can and let us know, it is a simple straightforward swap, linking out requires more and I'm not going to explain to you how, that's left for an engineer.