combi boiler reduced flow after mag one internal replaced

12 Feb 2006
Reaction score
United Kingdom
I have a grant combi boiler with a combimate and Mag One fitted it the system. Recently the Mag One started leaking. Heating engineer replaced whatever is inside and cured the leak. Since then, the shower is feeble and there isn't enough hot water to overcome the cold water pressure in the basin mixer tap. The boiler still fires up and gets hot, heating the rads but regularly overheats and cuts out. Could it be that he did something wrong with the Mag One? Any advice appreciated, thanks.
Sponsored Links
The mag one is only on the heating side, so unlikely engineer has done anything, unless there was call to turn the water off?
Thanks very much for your knowledge, the mag one must be a red herring. Any ideas what might cause my problem please?
  • Like
Reactions: CBW
Sponsored Links
Have you had any other work carried out recently?
Have you contacted your engineer to ascertain what work has been carried out?
Sounds like a blocked secondary heat exchanger.
you dont say which boiler you have , it might be that the engineer turned an isolation valve off and its not back on properly if it is a combi
  • Thanks
Reactions: CBW
its a grant, not sure what model. Today I emptied the balls out of the combimate and cleaned behind the red plastic inner which was thick with whatever the balls are made of. Thought that might have solved it but the flow is only slightly better at the showers but still not enough to run hot through the tap. However, the boiler has not gone into overheat since. there is a little round black thing that looks like an automatic vent? I took the bleed screw out but no water came out. Is that correct? There is also a large stopcock type valve in the middle looking down on the boiler, that is all crusty as if has been leaking very slightly for ages. Its due a service in June so I was hoping to hang on till the engineer comes then.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links