Bosch heatslave 20/25

[chrisjohn236]

Hi, I have a bosch heatslave 20/25 oil fired boiler with a slight problem, the central heating works fine but the hot water out of the tap starts off warm but soon runs cold or just cool, could this be the heat exchanger, any body help please. Thank you, Chris.

 

[kimbo]

It could be the flow switch not working or the diverter valve could be stuck, is the 3 port valve head a light grey plastic one, if so a common problem with these is that the piston inside of them stick.

 

[SimonG]

Flow switch, heat ex, diverter (3 different types), pcb sticking relay

 

[WHPES]

From experience, I would suggest heat exchanger is fouled with black sludge. Requires strong acid to clean out and not always successful so sometimes a replacement is necessary. You would also require a powerflush of the system if this is the case or it will just keep happening. However it could be something else as well.

If you have one of the diverter valves with the grey plastic heads, the valve plungers require servicing by a technician every few years. When the head is removed, they willl see a plastic insert which you unscrew with a special tool (or you can make your own as I have). The inside of the valve and the actuator needs to be cleaned and re-greased with heavy silicone grease -literally smear it on thick. Word of warning, be careful not to lose the circlip as it can go flying off in any direction if removed!

 

[Bunker]

the valve plungers require servicing by a technician every few years. When the head is removed, they willl see a plastic insert which you unscrew with a special tool (or you can make your own as I have). The inside of the valve and the actuator needs to be cleaned and re-greased with heavy silicone grease -literally smear it on thick. Word of warning, be careful not to lose the circlip as it can go flying off in any direction if removed!

Ya learn something new every day

 

[SimonG]

That's when/if you get the cartridge out in one piece

 

[Bunker]

Hi, I have a bosch heatslave 20/25 oil fired boiler with a slight problem, the central heating works fine but the hot water out of the tap starts off warm but soon runs cold or just cool, could this be the heat exchanger, any body help please. Thank you, Chris.

Firstly Im sorry to hear you have one of those, must have been fitted by a Gas fitter...

Secondly: Try these:
[Engineers very welcome to duplicate with amendments/ additions to below - its late and I might get it wrong....]
Open the top and CAREFULLY feel the temperature of the 4 pipes coming off the plate heat exchanger:
The 2 bigger ones are the primary flow and return - with the boiler running (careful: HOT HOT HOT) and the prog switched to Hot Water - do both pipes feel the same temp? (best method of course is with a thermostatic probe of some sort).
If no, does the hot water control stat (dial) click? when it does, is the circulating pump running?
If yes, then it looks like the heat passing through the store and plate isnt obstructed so all good on that front.
If above is ok, get someone to turn a hot tap on, you should hear a click at the flow switch.
One smaller pipe is the mains coming in cold, the other is hot water out. Does the hot water out feel the same temp as flow and return at first?

I found a few times that the heat exchanger has been scaled up so the heat cant get out of the store and the HW control stat constantly satisfied so the boiler doesnt fire, pump doesnt run so no heat gets exchanged. There is a way to check this but not for non-engineers ears Im afraid.

 

[Bunker]

I love it when the op takes a sec to say 'ta for the effort'...

 

[SimonG]

Cheers Bunker

 

[Bunker]

 

[chrisjohn236]

Hi thanks for the help from every one, been away and only just seen the replies will try as suggested.