How to diagnose the cause of pump over

[preece]

Recently my CH system is getting Pump Over, but I unsure how to figure out the cause.

1. Seven minutes after switching on, hot water pours through the vent into the CH header tank.
( Nb. the pouring is like a tap turned on ).
2. This happens with either water & heating, or just water.
3. The system has hardly been touched for 30 years.

I'm thinking I must have a blockage and the pump is forcing water up the expansion pipe.

But I would also like to be sure there is no other possible cause. If it is a blockage how would I locate and fix.

Also to help my understanding, what causes the pump to switch on - is it triggered by a thermostat in the boiler ?

Thanks for any help,
Tim

 

[Chuck]

Check the ball valve in the feed/expansion tank isn't leaking, i.e. the level stays below the overflow to the outside at all times.

Otherwise, as you surmise, it is almost certainly a partial blockage (of magnetite) in the section between the vent pipe and the rest of the system. The 7 minute delay will be the time needed for all the water in the system to have warmed up and expanded to the point that the pump over can start.

Discuss with your plumber the pros and cons of power-flushing vs a more surgical approach. 30+ year old systems that have been neglected are often rather fragile and a full power-flush can be the final straw.

 

[Gasmk1]

possibly a blocked cold feed

 

[preece]

possibly a blocked cold feed

Yea I read that blocked cold feed could be the cause, but I can't understand why a blocked cold feed would cause the hot water to gush out of the vent when the pump kicks in.

Presumably the cold feed here means the cold pipe as it leaves the f&e tank, so a blocked cold feed would simply prevent the CH system from refilling.

Tim

 

[townfanjon]

It will be also down to where the pump is in relation to the feed and vent . Locate the feed and vent and run a magnet over it , if its blocked with magnetite it will stick

 

[PhoenixServices]

The cold feed is also where the heating water expands up when your heating and hot water is on. If this is blocked then it goes up and over the expansion pipe.
Check with a magnet where the cold feed tees into the system.

 

[preece]

I really don't really understand how it could just be a cold feed blockage. If it was due to water expansion then I would only expect a small amount of overflow, not the large amount of gushing water that I actually see.

I suppose if it's often the case that blockage occurs where the cold feed tees into the system, then the system flow itself might have become blocked ?

I'll try magnets.

Tim

 

[RoryD]

Sludge and configuration will do this. Have an experienced engineer take a look and advise because either way its going to cost money mate.