Bubbling noise in house when Boiler comes on at 7:00AM

[JohnP2712]

Hi

I have a very persistent bubbling noise coming from my central heating system. The system worked fine until I replaced a radiator last Summer.

The system is conventional with the two cold water tanks in the loft and is powered by an oil fired Worcester boiler at the lowest point (kitchen). I have it set to heating only, hot water being provided by economy 7 heating element in the hot water tank. Most of the system is microbore however some 7 years ago the boiler was changed and a new extension fed from it using conventional 15mm piping. It has all been fine for 6 years.

The noise occurs when the system starts up first thing in the morning. There is a loud bubbling that goes on for around 30 seconds that can be heard upstairs in the master bedroom. I have tried bleeding all radiators including the vent next to the hot water tank and the pump. I have done this around a dozen times. The pump only bleeds when running. Very ocassionaly I find a radiator that is only 75% full of water. Normally all is fine.

More recently the pump started to make a loud noise when running. To solve this I turned it down to its lowest setting (It was set to the middle setting before). The pump noise has abated but the bubbling remains. I have checked the cold water feeds. All is OK (I had to adjust the heating water tank ballcock as the level was high but its not filling past that point or anything suggesting a leak in the hot water cylinder coil.)

I am at a loss now.

Thanks!

 

[oilman]

It's gas in the system somewhere. Did you put corrosion inhibitor in?

 

[JohnP2712]

Hi

Thanks for your reply. Yes I put three lots in

 

[JohnP2712]

I hear it in the morning and ocassionally during the day in the lounge. But its really bad when the system starts up from cold

 

[wilhelm]

might need a target board in heat ex, or might be overfired?

gawd knows..

 

[JohnP2712]

Thanks

This started after i replaced an old radiator. I assume being overfired would start after a service. And the really loud bubbling happens before the heating water gets hot. Basically the second the pump starts up.

 

[wilhelm]

Yes, it would be after service,

do your rads bleed ok? cos i m thinking blocked cold feed. also do your rad pipes go underground into concrete?

 

[JohnP2712]

Hi

Thanks for your reply

The rads all bleed OK. The pump does not. It only seems to bleed when running. None of the pipes are under concrete

 

[wilhelm]

maybe pump valves are blocked? I have had it. Drain down and rip em off (ooer) and check em out. Although symptons to this was carp heating .

But hey nothing to lose.

 

[JohnP2712]

Hi

Interesting thought

Thanks

I will try that

 

[JohnP2712]

If it comes to that I might as well fit a new pump at the same time as this one is over 15 years old. Which is better for this an auto vent type or normal do you think

 

[wilhelm]

Grundfoss 15-50 , unless you live in a castle....

 

[JohnP2712]

Hi

Sorry to be a pain. Defintion of castle? I have 16 rads (9 of these are doubles) with the extension six years ago. Should I go for a 15-60?

BTW the exisiting pump is a 15-50.

Thanks