Noisy Boiler after Radiator replacement

[davsy]

Have just replaced a radiator (double in place of a single) on a pumped vented system and since then have had very noisy boiler, very hot water back up into the F&E tank and the burner only runs for a few seconds then stops.

Building is a Bungalow with a Dormer conversion, the Boiler is in the loft, F&E tank is about 18 inches above boiler, pump is on the flow line downstairs in a utility cupboard with the HW tank, motorised three way valve and timer etc. The boiler I think is a Myson, not very new!!! There are 9 radiator in total 2 upstairs 7 down, all are fitted with isolating valves only, no TRVs

The radiator was replaced whilst the rest of the central heating system was operating, (just isolated at the valves) after completing the installation, shut off the central heating, slowly opened the feed valve to the new radiator, removed air from bleed screw, after all obvious air removed then opened the outlet valve from the radiator. After switching on the central heating again radiators got hot fairly quickly then boiler started "banging" and the F&E tank became very hot. Since then not able to get the system working again.

It sound to me like a circulation problem (when I try running the system I can get a bit of hot in the CH system but only sufficient to heat about half of 1 radiator upstairs nothing downstairs or the DHW tank, all the other radiators are cold) is it possible that when I opened the water to the new radiator, it may have been a bit quick and pulled in a slug of air which is now causing a problem. (not sure if this is possible with a level in the F&E tank)

What is the best way to push out an airlock (if anyone agrees that this could be the problem)

I have checked that the F&E tank is feeding water to the boiler by draining a low point in the CH system and checking the ball float operates fine.

The 3 way motorised valve is operating fine, I have checked by selecting either only CH or only DHW.

There is a bleed valve directly above the boiler on the return line which I have opened to find a good flow of water.

Do the symptoms sound like an air lock or is it some other problem, the water was reasonably clean when draining the old radiator.

A further question I have is should the bypass valve at the Grundfos pump be closed, slightly open or fully open.

I look forward to any information you can give.

Cheers

Steve

PS> the Bungalow is my OAP parents so have left them in a cold house tonight so really need to get something sorted ASAP, Emergency callout is a bit over expensive for a couple of OAPs on benefits!!! so if I can find a solution would be great for all concerned

 

[Gasman1015]

Yes, does sound like an airlock, boiler or horizontal run from boiler.

Have you bled the pump.
Is their a bleed valve on the hot water circuit just above the three way valve.

Try running the system with the boiler thermostat off, bleeding pump and boiler while its running to force airlock out, its a case of listening to the flow through the pump, that gives a quieter woosh as opposed to sudden rush of water.

Bypass, slightly open.

 

[chrishutt]

I'm doubtful about an airlock because you didn't drain the system or do anything else that might have introduced air. Yet something seems to be blocking circulation through boiler. Could it be sludge in the system that has been disturbed, or maybe a motorised valve problem (try it on manual setting) or a failed pump or boiler thermostat?

You say that the feed and expansion tank gets very hot. Is that the result of hot water emerging from the vent pipe (the pipe that inverts above the tank)? Try opening by-pass fully to see if circulation then improves.

Thinking about it a bit more, the symptoms are mostly consistent with a failed pump. Check that first.

 

[davsy]

Thanks for the replies.

I have been back this morning.

There is a bleed valve downstream of the motorised 3 way valve on the CH circuit, this always seems to have a god flow of water only, no signs of any air.

However when I looked this morning when it was all very cold I noticed that there was a fair bit of air coming out of the bleed at the boiler return connection (except for the F&E tank this is the highest point in the system) I left the bleed open with everthing else shut off and could hear the F&E tank filling which I assume was wtare replacing the air that was being expelled through the bleed. After bleeding all possible air from this and then all the radiators (radiators did not appear to have any air) I started up the boiler on a low thermostat setting.

The banging has now gone and after a few minutes I raised the boiler thermostat setting to maximum still no banging. Everything seems to be circulating hot now and the boiler is firing continuously without any noise.

However I did notice that the system seems to take an age to warm up, now thinking that it was part of the same problem I asked mum how long does it normally take to warm up, (they turn the main room stat down to minimum every night) she said "well it is normally afternoon by the time the main living room radiator gets warm" to me that sounds very long, surely the radiators should be getting at least a bit warm fairly quickly.

At the moment the boiler stat is on full setting and is firing constantly, I will go back in a few hours and see what is happening when everything is warm.

This raises two questions, firstly is it normal for this type of boiler to be run at full setting and secondly if I get there and the boiler is still firing continuously but the radiators ar not all hot do I assume there is a boiler problem, it would indicate to me that it is undersize, but if the boiler is cycling on and off but the radiators are still not all hot there is some other form of circulation problem.

Look forward to your response.

Cheers

Steve

PS:
Boiler is a Myson WM30/40BF installed circa 1990
Pump is Grundfos 15/50 which is approx 7 years old (installed when a new Hot water tank was installed)

 

[davsy]

Need to clarify my last post.

When I said that "everything was now circulating hot" I mean hot water is leaving the boiler hot and most of the radiators are warning up, DHW is also upto temperature. Still waiting for all radiators to reach temperature.

cheers

Steve

PS. My typing is crap this morning

 

[Gasman1015]

Check the bypass setting