Expansion pumping over

[denniswiseman]

Hi

I have an S plan heating system with a deaerator fitted and a Grunfos 15-60 in a 19 rad system
When I run the pump on full it pumps over the expansion
The cold feed isn't blocked
It doesn't pump over on hot water only
This is a new occurence as it never happened before

I am a retired heating engineer and have seen most things but have never seen this before
I am considering a powerflush but would like to pick the brains of the many before I jump in

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Hi Dennis
What type of deaerator have you got?
Most people would suggest cutting it out & pipeing it back up (in 28mm if you can).

If the system is dirty it will alway accumulate in the air separator due to the low water velocities I doubt very much whether a power flush will clear it out.

The

 

[denniswiseman]

Thanks for the reply

I think it's a 22mm airsep image attached
I can't see how the HW side is OK and not the CH

 

[finchy01]

As previous. It will almost definitely be caused by the air separator. The hw will have far less restrictions so will probably cope with the flow. A power flush and cutting that out normally cures it. Try opening the bypass when heating g is on and couple check if it still does it. Also, is there a rad without trv? It could be they're all closing down if not. Probably teaching you to suck eggs but that's just the most common faults I've seen.

 

[gassafe]

Looks like an old system, is the heating 2 port opening fully?

A repipe of the feed & expansion should cure it, maybe a combined feed & vent?

 

[denniswiseman]

Thanks for the replies

I don't have a bypass as there is no need for a pump overrun
I don't have any TRV's
I assume that the MV is operating correctly as when I run HW only it doesn't leak past and when it's calling for heat the rads heat up, however previously the pipe to the CH MV was furred up quiet bad. I replaced this but suspect it may be partially blocked again, would that cause it to pump over when on the high speed?
The system is probably 25 years old and trouble free apart from two new boilers
There is inhibitor in the system

Would a power flush clear any partially blocked pipe close to the CH MV

 

[jam1979]

U could re pipe it into a H to see if that cures it

 

[denniswiseman]

It was origonally like that, I converted it to fit the deaerator, that's why the pipework is out of line

 

[hammerheat]

Cut the air sep out and do a combined feed & vent

 

[denniswiseman]

Is a combined cold feed and vent now considered good practice

 

[denniswiseman]

I have just tested my pipes in the airing cupboard with a magnet and I have a build up of magnetite scale in them
What would be the best way to treat this apart from repiping it