Heatslave 18/25 no HW but CH is fine

[e5c0rt.mk1]

Hi, i have a external heatslave 18/25 oil boiler. The CH is working fine but the HW only works for about 2 minutes before it goes just warm, the only way to get it hot is to have the tap barely running. Its like the water is going through the boiler quicker than it can heat it.

I have removed the actuator from the diverter valve and manually changed the flow from CH to HW and it makes no difference. The radiators dont get hot with just the HW on.

The flow valve is working as the boiler comes on, when turning the tap on

I am going to remove the heat exchanger next to see if it has and blockages.

Does anyone have any suggestions on what it could be.

Thanks Owen

 

[oilhead]

If lower flow rate produces heat, then DHW heat exchanger sounds suspect.

 

[e5c0rt.mk1]

I've put a brandnew diverter valve on the boiler and it has made no difference.

I have also took the heat exchanger off and cleaned it out with spirit of salts. A bit of crap came out of it but nothing major. It has improved it a little bit.

Its hot (not boiling) for about 10 minutes then it goes cold.

I have felt the pipes in the boiler after the water has gone cold and the HW out is cold but the CH pipe out is warm.

Has anyone got any ideas what is up with it?
Thanks

 

[Terrywookfit]

What size nozzle is fitted to the burner.
What is your H/W stat setting

The boiler is designed to give 90 litres of water at a 40° temp rise with a max flow of 18 ltrs / min.

 

[oilhead]

The CH pipe will be warm from conduction. 5 mins running at 18 litres/min will use up your 90 litres faster than you can replace it, and that is only at a 40o temp rise. What are you running for 10 mins? Is it a bath through an oversize tap?