Cold radiators - Baxi back boiler gravity fed system

[hands2bfree]

Long story ill try to supply all the info:

moved into house - evident the heating had never been touched since 5 years ago when a new baxi back oiler was installed, mix ages of rads throughout the house.

the system is gravity fed

pump working but not sure how to bleed- do i just remove the disc cover?

first, down stairs rad in living room never got hot
second, box room was cold - rad bleed valve was rounded over - so could not bleed system
third, conservatory rad cold.
fourth, dining room and 2 bedrooms rad hot

I replaced the box room rad, but system still same after bleeding

I emptied the system through and filled up + inhibitor.

Still same issue with rads, but with knocking = plumber recommended a solution that that disperses air locks.

poured the solution in and then all rads went cold.

tried heating non stop on high for a few days but no results.

i emptied the system and put clean water in, but still no warm rads.

but i hear knocking again.

any ideas would be welome

Read more:Cold radiators - DIYnot.com - DIY and Home Improvement​

 

[jtsplumbing]

You seem to have a air lock on system or a faulty pump, is pump getting very hot ?? if so remove large center screw from pump, put in small screw driver , you will feel if pump is working, try this first and see what happens.

 

[hands2bfree]

Thanks for replying - yes the pump is rotating, not too hot - touchable.

 

[jtsplumbing]

Ok motor is working but its poss that impeller has snaped off, if its an old pump may be an idea to replace this first.

 

[hands2bfree]

Ok, if i remove the pump is it possible to inspect to see if impeller is intact?

 

[jtsplumbing]

yes you will see impeller in pump try to turn it with screw driver or switch it on if it runns OK make sure its faceing right way .

 

[hands2bfree]

Thanks, ill give it ago latter this evening when im home.

if the pump is ok, are there any other things i can do?

 

[jtsplumbing]

You may just have a bad air lock in system , has it ever work`d ? what area are you in ?? may be one of the guys on here could call round and have a look for you

 

[hands2bfree]

i have only been in the house a 2 years, never worked properly.
i live in Southend on Sea, Essex.

 

[jtsplumbing]

To far for me ! deep depths of Devon, may be one of the Essex guys can help ! do they still were white stiletto`s in Essex ! I am talking about the gas engineers !!:49:

 

[hands2bfree]

lol if they do and there female i wont mind them coming round to help:juggle2:

 

[tipintim]

System needs replacing?
Is the colour of the water in the system muddy, brown in colour?
Is the pump the correct way?
is it an old myson water mover or had a replacement pump fitted?
Turn speed down on pump?
Have you got a primatic cylinder?

 

[tipintim]

Sorry mate, been reading other threads. Needs a power flush, maybe to start.

 

[hands2bfree]

System needs replacing?
Is the colour of the water in the system muddy, brown in colour? - yes
Is the pump the correct way? - yes (directional arrows on pump)
is it an old myson water mover or had a replacement pump fitted? - not sure seems about 5 years old
Turn speed down on pump? - the pump is currently at top speed, should i turn this down?
Have you got a primatic cylinder? - I have 2 tanks in the loft, so i would say no.

 

[tipintim]

Ok.
System is drawing in air
Pump on flow or return
Try turning pump down to 1
not primatic
Vent, cold feed blockage

 

[hands2bfree]

Pump on flow or return - i will have to check to determine this one - I know the pump is located next to baxi boiler downstairs and thus will pump the water up, so probably flow?
Try turning pump down to 1 - ok i will change it when i get in
Vent, cold feed blockage - I presume i vent via bleed valves?

 

[tipintim]

oK.
Is the return pipe as hot as the flow.(within a few degs)

 

[hands2bfree]

i will have to check when i get home.

 

[hands2bfree]

update...set pump to minimum speed,
when i switch the heating on there is a popping noise coming from around the boiler pump area..?

the pipe inline with the pump is cold which i believe is the flow.
the pipe of the same diameter next to the pump which i believe is the return is cold.

there is another larger diameter pipe next to these which is hot

all of the rads upstairs baring the main bedroom are getting hot
all the rads down stairs are cold

 

[hands2bfree]

bump mmmm bump

 

[jtsplumbing]

What about hot water ? if you turn off pump and just run boiler for hot water do the pipes to the cylinder start to get hot ? sounding like you have a sticking pump.

 

[hands2bfree]

hot water has been very hot as i have had the heat high.
due to this it may take a while to find out the answer to that question.
once the pump has run for a minute or so that popping stops

 

[Anton]

If the pump is ok, one other thing to lookfor is an anti-gravity valve on the heating flow off the boiler. It's a brass valve which in length, including the nuts is approximately four inches long. These are designed to stop the first floor radiators heating up via gravity circulation when on hot water only, ie summertime (assuming we get one)
They can get blocked up with crud/sludge etc and stop the radiators from heating.

 

[jtsplumbing]

Its a bit strange upstairs hot down stairs cold keep thinking its the pump, but these are just shots in the dark water must be curculating or up staires would not get hot, is the gas burner on boiler getting a good flame when on for heating is it the gas burner that is popping or the pump?

 

[hands2bfree]

i have left the ch running and now the rads are all cold, they lost there heat.
the flame is good.

ok this is what happens:

pipe with pump in line has a drain off tap on it.
pipe of same diameter runs next to it.

on start up the impeller slaps because it seems to be running dry.
the pipe running parallel gets really hot during this time.

after a minute the slaps stop, which makes the pipe that runs parallel cool down and then both pipes are cold.

now and again the pipe running next to the pump gets warmer - i guess this is when water is passing through it rather than air

should i drain the system?
or should i shut off all but one TPV?

 

[hands2bfree]

bump mmm bump

 

[tipintim]

Sounds like you have got a blockage in the boiler/pipework. Try chemically cleaning the system. Put it in and run for a few days.
Is the pipe work on the ground floor burried in the concrete?
Can you post photos of the set up you have

 

[hands2bfree]

the pipe work is buried in concrete im afraid.

ill post some photos

ill try chemically cleaning

thanks for your help!!

 

[tipintim]

Went to a job recently where the pipework was burried. No way of draining muck out and struggled to flush because it was a one pipe system.
Customer then remembered there was a drain off in the garden for this purpose. Have a look around the out side of your buiding. His was hidden by a step!!

 

[hands2bfree]

the only other drain off i have is at the boiler, but ill look around