D
diamondgas
Hi Ian ... hmmmm ... re-read again and your conclusion sounds logical. Thing I'd be doing to check that the diverter was operating correctly is, from cold, hand on the return pipe. If it heats rapidly then it isn't shutting off the domestic circuit! Also checking out how rapidly the flow heats up. Ideally it should be gradual rather than rapid.
Regards pipe sizing You do have at least 22mm coming from the boiler yeh?
Now i know you've said you've checked for a filter, the manu instructions say there's one in the return connection furthest right! It may be incorporated in the valve itself! I've only ever worked on one Chaff of this era by-the-way!
Regards the pump, it looks like a grundfoss. You should be able to change the head for a 15/60 no problem. You can purchase the head on it's own, about £60...
You say the first three rads are turned off. Try the circulation with them turned on see if makes any difference just to rule out or in a blockage beyond these three radiators.
I''m edging towards the diverter valve as most likely problem, dislodged pump impeller maybe then beyond that a restriction elsewhere! Temperatures differences can tell a lot about how the boiler is working! Oh, bye the way! When your feeling the return pipe check the return above the pump into the boiler and the heating return under the boiler. If there's a huge difference between them then the diverter comes more to focus once more! The bi-pass is less likely to effect the circulation that much in my opinion!
Regards pipe sizing You do have at least 22mm coming from the boiler yeh?
Now i know you've said you've checked for a filter, the manu instructions say there's one in the return connection furthest right! It may be incorporated in the valve itself! I've only ever worked on one Chaff of this era by-the-way!
Regards the pump, it looks like a grundfoss. You should be able to change the head for a 15/60 no problem. You can purchase the head on it's own, about £60...
You say the first three rads are turned off. Try the circulation with them turned on see if makes any difference just to rule out or in a blockage beyond these three radiators.
I''m edging towards the diverter valve as most likely problem, dislodged pump impeller maybe then beyond that a restriction elsewhere! Temperatures differences can tell a lot about how the boiler is working! Oh, bye the way! When your feeling the return pipe check the return above the pump into the boiler and the heating return under the boiler. If there's a huge difference between them then the diverter comes more to focus once more! The bi-pass is less likely to effect the circulation that much in my opinion!