Flow issues with a Potterton Heatmax Combi 28 HE

[iCannon]

Hi
I have a Potterton Heatmax Combi 28 HE that was installed in 2014.
Over the past year or so it has slowly had more trouble heating distant radiators.

It was serviced in February 2022 and given a clean bill of health, however since then it now only heats the two nearest radiators and at a much lower temperature than the flow from the boiler.

I suspect the pump, but so far the one quote I had to replace it was for £600 which seems absurd ( Part Number: 7722642 ), and that's £600 that could just go towards getting a new boiler, considering it's already over 8 years old.

The pump still makes a noise like it's doing something but, the other radiators aren't getting warm and most radiators don't even feel warm at the flow, never mind hot.

One thing I noticed today is that the one radiator inside the main part of the house that gets heat is currently much colder at the bottom than at the top. I'm not sure if this is indicative of a restricted/blocked return, dying pump or what.

(the only other radiator that is capable of getting heat is one in the extension in the foyer by the back door, it's a small 1'x1' single panel and I've closed both the flow and the return on it (it's not part of the main loop), to try and get the one useful radiator to provide more heat to the house).

Given the callout charge, I'm reluctant to pay up for results that aren't a sure thing before doing everything I can myself to try and diagnose the problem

My own plumbing experience is dated at best, my Father was a plumber/gas fitter when I was growing up, and I spent a lot of years doing jobs with him, so I've replaced a lot of boilers, radiators, and your typical run of the mill jobs, including doing most of the heavy lifting getting this current one mounted 8 years ago, but that'd have been the only plumbing work I've done in over 20 years, and with my father no longer able to advise/supervise, I'd rather stick to diagnostics and pay a professional to do a good job (that latter part hasn't always worked out over the years, but I live in hope.

Any assistance is appreciated.

 

[iCannon]

[previously asked about valve alignment to double-check current status, I checked with the manual, it's not an issue.

Everything set to open except for the one valve that fills the boiler.

 

[iCannon]

I've popped a few valves off the radiators and opened them into a bucket.
Water ran clear and at pressure.

Leaves me more sure it's the pump but still would appreciate anyone helping rule out other possibilities, or knowing how to test the pressure of a pump that still pretends to work but doesn't seem to move water meaningfully.

 

[Deleted member 120897]

I would have a look and see if there’s a mesh filter on the return on the boiler, which if one is present and blocked could give your symptoms.

 

[iCannon]

I think it only has the magnetic filter, but I'll check that tomorrow.


Checking the 22mm flow from the boiler it already feels about 5 degrees cooler just 1 foot down the pipe.

 

[Deleted member 120897]

Checking the 22mm flow from the boiler it already feels about 5 degrees cooler just 1 foot down the pipe.

Check the diverter then - motor and valve

 

[iCannon]

Check the diverter then - motor and valve

Great suggestion, is there a way to test it without just stripping and replacing it?
While it doesn't look like a complicated job to replace, I'd rather wait on a professional at that point.

 

[Deleted member 120897]

Motor can be tested visually or and with a multimeter. If you can disconnect it it should move in an direction out on demands.

 

[Deleted member 120897]

Sorry, meant to say about the valve - make sure the pin can move up and down, make sure there’s no leaks from it.

 

[iCannon]

Sorry, meant to say about the valve - make sure the pin can move up and down, make sure there’s no leaks from it.

The diverter valve was rusted at the pin to that point that while it "switched", it had slowly lost the ability to fully change the flow to the heating over time, thus fewer radiators in the line got hot over time and eventually, none did.

It looks like there was just a really slow leak, enough that no water ever dripped out, but the valve generated rust.

Apparently, it should have been picked up in a service, and despite it being serviced in February 2022, it wasn't even commented on.

Thanks for the insight and pointers (although without me saying anything the plumber I hired picked up on it instantly), I just wanted to get back to you, that you were correct.

 

[Deleted member 120897]

The diverter valve was rusted at the pin to that point that while it "switched", it had slowly lost the ability to fully change the flow to the heating over time, thus fewer radiators in the line got hot over time and eventually, none did.

It looks like there was just a really slow leak, enough that no water ever dripped out, but the valve generated rust.

Apparently, it should have been picked up in a service, and despite it being serviced in February 2022, it wasn't even commented on.

Thanks for the insight and pointers (although without me saying anything the plumber I hired picked up on it instantly), I just wanted to get back to you, that you were correct.

Excellent thank you for taking the time to give feedback, not everyone does.