Central heating - issues following radiator swap

[Ian010778]

Hi there everybody, this is my first post here. Hopefully I can get some help please?

Last weekend I swapped the radiators in my upstairs bathroom and en suite for towel radiators but I now have uneven heat, banging and crashing sounds, the boiler is cutting out (assuming over-heating), and I have uneven heat across the system.

Here's the story and what I've done so far.

I isolated and drained each radiator, tied the ball cock off on the header tank in the loft, and drained the top half of the system via the feed and return pipes in the bathroom and en suite.

I then extended the plastic pipework (its a modern house - about 6 years old) to neatly connect and mount the towel radiators using new TRV and valve sets.

I left the new towel radiators isolated whilst I re-filled the system as follows.

With all TRV's around the house open I released the ball cock so that water started flowing into the header tank and I also dropped a bottle of inhibitor in to the header tank.

One at a time I then opened the lock shield vales, TRVs and bleed screws on the new towel radiators, allowing them to fill with water and I bled them until water started appear.

I also bled all of the upstairs radiators to make sure all air was out and the system was filled up. This is the second time I've part drained and filled the system in this manner this year so I didn't think I'd have any problems.

I did have one joint in the en suite that was weeping a little so I tightened this up the day after and this is now dry.

However, since doing this the following is happening:
1. I'm getting a lot of banging and crashing sounds from the airing cupboard and boiler when the boiler first fires up (HW and CH);

2. The radiator that is nearest the boiler in the kitchen is failing to get hot although the pipework on the TRV side of the kitchen radiator does get hot;

3. The remaining downstairs radiators are getting warm but incrementally the radiators get hotter the further up the house I go and the one on the landing that's nearest to the airing cupboard gets really hot; and

4. The boiler is cutting out after a few minutes of running and then constantly stopping and starting (I've turned the thermostat up so I know it's not that causing the system to stop and start).

The uneven heat prompted me to bleed all radiators again but there was only a small amount of air released from the landing radiator. All other radiators show water coming out as soon as I back the bleed screws off.

Last night I had a Google around and this led me to turn the system off, bleed the pump and the thumbscrew valve on the feed into the hot water cylinder coil as well as resetting the boiler and bleeding all radiators again but there was no air released from any bleed points and this morning the situation hasn't improved.

Any help would be really appreciated please - the system is a gravity fed vented system and the boiler is an ICOS HE12.

Thank you everybody


Ian.

 

[ServiceNumpty]

Did you bleed the pump.

 

[ianmcd]

sounds like you either have an airlock or you have let some crud from the bottom of your F&E tank into your system and now have a blockage

 

[Ian010778]

Hi Mike, yes I definitely bled the pump and no air escaped - just a trickle of water.

Ian, any tips on unblocking or removing the airlock?

Thanks both for taking the time to reply - appreciated.

 

[ianmcd]

if you have a drain off point at the lowest part of the system and have an outside tap I usually try filling the system backwards i.e. connect the outside tap by a hose to the outside drain down poing and force mains water up till it comes out of the overflow, lots of things to try but nothing guaranteed to work , sometimes if your pump isolation valves are the gate valve type then reversing the direction of the pump can clear it but dont attempt this if you have ballofix type valves they will leak

 

[Ian010778]

Cheers Ian,

This has always baffled me as I've never been able to locate a proper drain off point on any of the radiators or under the kitchen sink/around the boiler. When I've drained the system before I just do it via one of the radiators by opening the TRV and lock shield over a large bucket that I fill and empty repeatedly until the water stops. I guess this is what you get when you buy cheap modern houses

I'm not sure regarding the valve types so I won't do anything like that unless I'm absolutely sure - thanks for the advice on this.

I have realised that when I filled the system up Sunday afternoon I did it with all bleed valves shut - assuming this is similar to filling a car's cooling system I would usually have at least the highest bleed valve open as the water is entering the system so I'm going to try draining the top half down again tonight but make sure I have the highest bleed (on the hot water coil inlet) open as well as the bleed valves on the pump and the first radiator on the circuit (landing).

Hopefully, if it is an airlock, emptying and re-filling with the bleeds open will clear it but if I still have issues I guess it's pointing more toward a blockage.

Thanks for all of your help Ian.

Ian.

 

[Ian010778]

UPDATE - but still having problems

Hello all,

After a lot of perseverance (system drain, clean the F+E tank, chemical clean and re-fill, and power flushing the kitchen radiator) I've made some good progress with this.

All radiators are now getting hot and everything is running smooth and quietly.

However, the ICOS HE12 boiler in my system is still not behaving.

With only the HW turned on all is fine but as soon as I introduce a call for heat from the CH the boiler burns for about 15 minutes, stops burning, goes through the cool down process and immediately re-ignites rather than just circulating.

I've changed the control thermistor in the boiler and this didn't help. I also tried a new valve head on the Danfoss CH valve and this didn't help.

When the room stat' gets up to temp' and the call for heat goes away the boiler is fine - it cools down and returns to status '0' with no burner light activity.

So, I'm at a bit of a loss now as I think the boiler is fine due to it behaving perfectly on HW only but as I've completely drained and cleaned the CH system and everything's getting hot now I'm confident there's no air or blockage present but it's almost as though there's some sort of mis-match between temperature readings when the CH is on that's causing the boiler to 'think' it's up to temp, realise it's not therefore it's continuously in a cycle of burning and re-igniting when the CH presents a call for heat.

Any further help would be really appreciated please.


Ian.