CH failing - cold feed blocked ?

[datamile]

hi,

Our CH is failing, its a pumped open potterton 80 with 4 rads upstairs and 4 downstairs and it has been working fine for 15 years.

The has alway been some air in one of the upstairs rads, it bleeding it has left it ok. However its been rented out the last 3 years, and tenants now tell us that upstairs has rarely worked, and now the heating has failed completely.

ok, checking the system. The boiler runs ok for about 5 mins, and the first radiator starts to warm up, and then the boilers cuts out as it does appear to be able to get the hot water out of itself.

Now when I checked the upstairs rads, that all appear to have a large amount of air in, and its very hard to bleed any of them to get water. The pump is spinning, and the pipes do get hot either side of the pump.

So I think air lock, and remove one of the downstairs rads to drain the system.

This is where it gets interesting. The system refused to drain (no water out), unless I released the bleed screw on another downstairs rad. All the upstairs rads had their bleed screws out.

Also the header tank level never went down at all.

about 10 mins after the boiler cuts out, you hear an amount of water returning to the boiler. (gurggle gurggle)
After all this I'm think either

1) Pump impellers are kn*ckered - Could change the pump, but if air caused it to run dry, then another set would fail.

or

2) Blocked cold feed. - how do I detect this , and/or fix it ?

or

3) whole system sludge up. - Is it worth hiring a power flusher from hss and going it a go?

Any other suggestions ?

 

[doitall]

Can we assume it gets a yearly landlord safety certificate.

Even though you own the building, you are not allowed to work on the boiler without being Corgy registerd.

draining the boiler/system out leaving the header tank switch on then it should refill or as you say the cold feed is blocked, and more info is required.

Sounds like the system has been neglected.

 

[datamile]

the plumber who does the safety cert was the one that checked it out. I tried to flush the system on his recommendation to see if that would remove the airlock.

The plumber couldn't get the system recirculating, and so wants to rebuild the system around the motorized valves as he thinks there is no bypass for the boiler overpump with the valves shut. ( quoted £600+ just to start that, and he's not even sure of thats the problem or will solve it). The system ran for 10+ years with no problems and the occassional drain down and inhibitor topup, but its not been done since the tenants moved in.

Just looking for second opinions before blowing £600 for 'maybe' solution.

Never used a powerfushers, and presume that they would clean out the system but would not solve a cold feed problem

 

[doitall]

Powerflush sounds as though it's needed and could clear the cold feed, otherwise it will need to be disconnected at a point close the where it joins the system.

powerflushing is not just connecting the machine up and switching it on, read up first before you start.

 

[datamile]

any tips/links

I was looking at the HSS one as they are near me. Not sure what connection you get. ( rads or pump )

It says

"Improves system circulation and heating efficiency
Each kit includes boiler adaptors, tool kit and 30m tubing
Connects to all 1/2" BSP pipes
"

given that I think there are two rad circuits , and the pump. I presume I should use the pump connectors if they given them to me, otherwise do I need to do both circuits separately ?

 

[ChrisR]

If you have hard magnetite sludge on the inside of your feed pipe where it meets the circuit, powerflushing may not touch it, depending partly on what chemicals you use. The only solution then would be to cut out the affected pipes and replace them. You'd certainly be better off getting rid of it first.

Magnetite is easy to detect from the outside of a copper pipe of course.

 

[datamile]

These instructions look ok.. looks the same kit as hss, but I don't know if they do the chemical.

http://www.kamco.co.uk/DetailedInstructionsCF30DDV.htm