Pump making horrible noises after fixing pipe leak

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I have an open CH/HW system with a gas boiler (one of those 70s/80s things with an ugly gas fire on the front, don’t know the make), HW storage cylinder, Grundfos Selectric 4 pump and Potterton EP2002 control panel. This is the first time I’ve got involved with CH/HW systems and I’m learning fast but, as you’ll see, perhaps making a few mistakes.

Recently I spotted a leak in a 15mm pipe leading to a radiator. I closed off the supply to the expansion tank in the loft and drained off water at the leaky joint (rather than at the drain point). After fixing the joint I opened up the water supply and switched on the HW. The boiler fired up but then shut down after about 3 minutes. 10-15 minutes later the Grundfos started making some ugly noises so I switched off the HW. The cycle repeats if I wait a while, i.e. switch on HW, boiler fires up, boiler shuts down a few minutes later, pump makes progressively more horrible noises.

While checking all aspects of the system I went to the expansion tank and found the lid had virtually disintegrated. On looking inside I saw loads of grot and filth floating on top! Under normal conditions this grot would stay on the surface and not enter the system however, because I drained the tank, I suspect the grot may have reached the pump and/or boiler and blocked the system.

I’d like to open up the pump and check it out but, having been quite an amateur up to now, would appreciate a “beginners guide” to the process. In addition, could the problems be due to air in the system? If so, how do I bleed the HW circulation (I’ve done the radiators)? Anything else I should investigate?

Many thanks.

Online pics of:
Cyclinder and pump, http://www.hooper67.plus.com/CH/cyclinder.jpg.
Close up of pump, http://www.hooper67.plus.com/CH/pump.jpg.
Boiler, http://www.hooper67.plus.com/CH/boiler.jpg.
 
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Ho hu... should read more of the existing threads before posting :oops:

I read through "Tepid HW & Rads - please give me a clue!" and founds tips from ChrisR and oilman on where to find the bleed value. I located mine and released a fair chunch of air. Now the pump is running smoothly and the pipes are hot in and out of the pump. Note that I've had to bleed a few times at intervals so I assume there was trapped air in various corners of the system.

Thanks to ChrisR and oilman, and for this forum.
 

COG

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That pumps had it,its at least 20 years young, a new grundfoss pump is around £35, personally i would cut out that section of pipe,valves and pump and replace the lot ,save a lot of stress later. Use 15/50 pump not a 15/60 the later is now more common at the merchants but may pump over at the tank, the 15/50 is the same as your existing pump. If your tank is galvanized not plastic then best to change it for plastic, if you can drain down freely from that point you may not have too bad a blockage if you can get it too circulate the a sludge remover should get rid of the rest ,if it does not drain freely you may have to physically clean out the cold feed to the boiler
 
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