Noisy system, Hot Expansion tank, Cold rads, Pilot going out

We are having heating nightmares at the moment.

Not combi boiler.
System really noisy for about a year. Banging, rushing, water trickles. Fitted new pump as found out old one was leaking and corrosion was there. Bled rads to try and get air out. Upstairs one bedroom has constant air in it. Can bleed and then needs bleeding again 20mins later.

After fitting new pump hall and living room rads were cold. Tried bleeding. Banging still there. Black sludge out and loads of air.

Living room one now works, hall has been on, but has subsequently gone cold again.

Everytime system bangs, the boiler fires down until the bangs pass, sometimes when fired down pilot goes out too. Told the firing down is a safety feature, but surely pilot shouldn't go out too.

Expansion tank is full of hot water.

Finally, when on Water only, not CH, the rads all get hot and the pump starts, wired exactly the same as the old one, but not sure if this problem has always been there as never really checked before. Boiler does fire down though when water reaches temp, even though room thermo may be higher.

Couple of plumpers we have spoke to keep sayings its all air in the system, and that it could take a while of bleeding to get out.

Any advice? Should we contact a heating engineer? Do they all charge call out fees?

Hot water in the expansion tank is either "over pumping", overflow from boiler output too short, incorrectly sited or pump pressure too high.
The fact that your boiler keeps shutting down is probably because the water in the heat exchanger is too hot resulting triggering the safety and also blowing out the overflow.
If the water isn't able to pump around the system due to a stuck valve or air lock then it will sit in the bolier and overheat.

Try checking the valves (single 3way or twin 2way ?) as the valve motor has a microswitch that controls the pump on/off signal. Isolate the electric supply, unscrew the head unit and see if the valve gear is free. If this is OK then carefully power up the system and see if the valve motor is working. If both are OK then reassemble it and revisit the wiring for the pump.

Ron, Thanks for your reply.
Last night we switched all rads off (both sides as some of the caps seem to be on the wrong sides, + and - dials are on the return pipes on some, the inflow pipes on others) except the back bedroom (the one the air always collects in) and the Hall (the one that has been constanstantly cold).

Fired up the system, and kept bleeding bedroom rad whenever it went out. Eventually when we got it to stay on and Hall became hot, we started opening up each rad one at a time.

There were some bangs, but eventually it went quiet, and all rads got hot. The system doesn't seem to have been balanced previouly as all valves on both sides were fully on.

The pilot for the first time has stayed on even though heating was on this morning.

If all stays well, we just need to see if expansion tank cools now, and then sort out why rads are getting hot when on water only. Someone suggested possible failed valve? My dad thinks the pump shouldn't run on water only, but it does, is this normal?

Thanks again

Jobee, with an "indirect system" the pump is needed for both water and heating as it needs to circulate it either around the coil inside the hw cylinder or around the rads.

Some older systems didn't use pumps and relied on the gravity difference of the hot output water over the cooler return feed. They aren't the most efficient and fitting a pump improves things greatly.

(car cooling systems are the reverse of a c/h system - see how far you don't get with a broken water pump or fan belt)

Hopefully you only had an airlock then. Fingers crossed!

You mention sludge. That will obstruct flow and do no good. Order a couple of bottles of system cleaner (Sentinel and Fernox are good brands) and one of inhibitor. When they arrive, flush out what you can of the loose stuff, then refill with cleaner and follow the instructions. Drain, flush, rinse. If still dirty you may need to clean again. When clean, rinse and refill with the inhibitor.

Carry on looking for design and build faults.

If you can afford £100 or so, get a Magnaclean which will attract and hold circulating particles (cleaning never gets it all out) which will otherwise settle in the boiler and wear out the pump.

Ron Gamma said:

Jobee, with an "indirect system" the pump is needed for both water and heating as it needs to circulate it either around the coil inside the hw cylinder or around the rads.

Some older systems didn't use pumps and relied on the gravity difference of the hot output water over the cooler return feed. They aren't the most efficient and fitting a pump improves things greatly.

(car cooling systems are the reverse of a c/h system - see how far you don't get with a broken water pump or fan belt)

Click to expand...

And just like older CH systems old cars never had water pumps they relied on the convection current through the big vertical radiator at the front. More power and less space resulted in cross-flow radiators and pumps.

stevesey said:

... old cars never...

Click to expand...

You're going back to the early days of motoring there, before the 1930's