Central heating blockage/flow problem

[bearmac64]

Hi to you all, I am new to the forum.
I have a baffling ch and hw problem which my plumber is unable to solve.
I have lived in my house for 12 years and the ch and hw water always worked reasonably well. The performance had begun to deteriorate over the last 2 years or so last summer I decided to flush the system. It is a simple open vented system with a single feed from and return to a Concord WRS boiler which is 30+ years old. When I drained down the water that came out was surprisingly clean. I drained until the system seemed empty then tried to refill. I then discovered that the cold feed was blocked under the the bathroom floor upstairs so I disconnected it and found a lot of black sludge where it teed into the boiler return. After cleaning it the system then filled up and the heating began to come back on with radiators warming up. Then the system went cold and the hot water would not work. I suspected a blockage remained around the cold feed and the boiler feed/return. I got the plumber to come and power flush which he has now done 3 times. Some sludge came out but since then the system will not work properly. Generally the rads upstairs will warm up, the downstairs remain cold. The hot water will not work, the feed into the tank warms up but the return pipe stays cold. The return pipe to the boiler is usually cold or just luke warm but the boiler feed pipe is red hot. The plumber has replaced the pump and the hot water tank (because it was leaking). The system often boils over when it comes on in the morning with hot steaming water venting into the small tank in the loft. I still suspect a blockage. Anyone have any ideas please? Thanks Iain

 

[gassafe]

Sounds like a pretty old system with an old concord boiler! Are there any motorised valves on the system?

If its been flushed and the cold feed blockage cleared with the system now filling up okay then it could just be a stubborn air lock or a blockage in the system somewhere..?

 

[bearmac64]

Thanks for your quick reply. Yes there are two motorised valves. The hot water feed from the pump has a tee off to the hot water tank. There is one valve on the teed off pipe next to the tank. The other is just above the tee for the heating. They both seem to work ok. I suspect a blockage too.

 

[bearmac64]

There are 2 motorised 2 port valves, one for heating and one for water. both are working as far as I can tell.

 

[gassafe]

Surely the plumber will sort the issues out if he has done 3 powerflushes... A powerflush cannot really be used to clear a blockage, it relies on a flow of water through the pipe etc for the cleaner to take effect.

Once you have ruled out air locks or circulation then its time to start cutting the pipework apart to trace blockage...

If there is no flow round cylinder or any rads then suggest blockage in main primary pipework from boiler to airing cupboard?

Try to get water circulating around coil first, its all 22mm pipework probably and should be no restriction...

 

[bearmac64]

Thanks gassafe. I agree with you, my plumber has been investigating the flow and return under the floor downstairs but I think the water is just not getting around the boiler loop which is therefore causing a back pressure in the system. In fact he disconnected a couple of rads and then the pipes at the opposite end of the remaining ones downstairs got warm suggesting to me a flow in the wrong direction. Everything comes together near the cold feed upstairs under the bathroom floor and near there the cold circuit joins in and remains cold. The tank and airing cupboard is downstairs right near the pump so all the return water has to go upstairs. I will try what you suggest.

 

[0304Driver]

Is it pumping over all the time the pump is running? ie water running out the open vent pipe in F and E tank. If the open vent and cold feed are piped correctly before the pump, and it is pumping over then there will be a restriction/ blockage between the open vent and the pump. I know you said it had been flushed 3 times but if it was blocked solid you would know when you were doing the flush, ie no Flow through machine.

 

[JusKel]

Have you tried putting the motorised valves into manual position ?
Also check that all valves are open, its possible some were left off after flushing.
As above, if it was flushed correctly then any blockage would have been noticed.