New stat, banging & bubbling?

[markdon]

Hi all, we have an older back boiler in our house, it did have a non digi stat but i have changed it for a digi one, checked the wiring and its ok.

Odd thing, now every time the heating gets to temp & clicks off, the boiler bangs and bubbles can be heard from the boiler and going into the tank in the loft.

Any ideas why changing the stat would do this?

Cheers.

 

[markdon]

Im assuming this is air in the system, ive tried bleeding the rads but theres no air there. Whats going on? Will this cause further damage to the pump / boiler?

 

[JohnD]

sounds like it is getting too hot and boiling.

have you wired the stat so it turns the pump off?

is it gas or solid fuel?

I am guessing it is quite an old system so it probably has a lot of sediment, sludge and limescale in it. You could give it a chemical clean and flush.

 

[markdon]

Its a gas backboiler that was fitted in 1995, i've had a plumber out who i know who drained the system, put sludge remover in, came back 4 days later, drained & added inhibitor.

Since thats been done its been ok apart from now and then there is a short quick rushing sound in one rad.

Then after 2 weeks i removed the old stat & fitted the new one, and since thats been changed when the pump cuts out there is a banging noise from the boiler & a bubbling noise which sounds like it goes up to the small tank in the loft (not the hw tank)

Any ideas?

Thanks.

 

[Biguns]

I think John D has hit the nail. The pump shuts down before the boiler or its got a pump overrun stat which is by passed or failed. Thus causing the pump to shut down the same time as the boiler. Then the residual boiler heat causes the water to boil,

http://www.nu-heat.co.uk/s.nl/ctype.KB/it.I/id.17055/KB.122/.f

 

[markdon]

So the new stat is shutting the pump off quicker than the old one?

I did notice there were three terminals on both old & new stats, they are both honeywell, the old one was wired up to a & c, where the new one is wired up to a & b.

I checked both manuals and i cant figure out why the old one was wired up that way, it should have been the same as the new one?

I will look into the pump detail to see if it has an over run feature. Could this be the pump knackered?

Thanks for the info.

Mark.

 

[Biguns]

The pump overrun stat is not part of the pump. It is part of the boiler wiring. The stat if it has one ( what is the make and model of your system) will be in the boiler assembly and the wiring to the pump will incorporate it

 

[JohnD]

it may also be that your new stat is set higher than the old one, so the water has less capacity to absorb the residual heat in the (presumably) iron boiler.

How long ago was it cleaned?

What happens when you bled the rads?

Is the feed to the HW cylinder pumped, or gravity?

 

[markdon]

It was cleaned out about 4 weeks ago, it was the week before christmas i think.

System is cold, start downstairs, bleed rads, no air at all apart from the bathroom and 2nd bedroom rads which are on a hot water loop so when hw is on, they heat up, dont know why but they always need bleeding every two weeks or so, will have to lift the floor to lopk for a leak, we moved in here in aug and its always been like that.

System is gravity fed woth small ch tank in loft, cylinder in bedroom 2, boiler and pump behind fire.

Thanks for your time.

Mark.

 

[Biguns]

Do the radiators get too hot to touch. If so it may be that simply the boiler stat has failed and the boiler is getting too hot. Then when the system shuts down the residual heat again bubbles to the F&E tank

 

[Agile]

Turn the BOILER stat down a little!

Just because someone has done some water treatment it does not mean that the water is now totally clean and all sludge has been removed.

We dont know what chemicals have been used and we dont know what the sludge comprised of. The chemicals used have to be chosen to deal with the particular water problem.

It could be that sludge has been moved into the boiler after being loosened by a chemical.

Tony

 

[markdon]

Ok thanks, i will turn it down, is there a rule for what it should be on? Ive not changed it since we moved in. Think its on 4. I am right in thinking this is the numbered dial on the fire? One to start the fire & set the level, this one (numbers 1-5 on it) and there is also a small grey knob, but im not sure on that one either.

The rads all have trv's fitted and are all on different settings, none of them get too hot to touch, i will check this though.

Thanks very much, i will report back tonight when ive adjusted it.

Mark.

 

[markdon]

Hi, i've turned the boiler stat down to 2.5, the room still gets to temp ok and the banging has stopped. The bubbling noise is still there, but alot less violent. Is there anything else i should look at?

Thanks again.

Mark.

 

[JohnD]

there is a fair chance it has sludge and scale in it. Short of paying hundreds of pounds for a powerflush, there are a couple of inexpensive DIY things you can try. First one is to use a sludge-cleaning chemical. It sounds like that has already been done. Without knowing what chemical it was, and what the results were, hard to know... but if you are in a hard water area and get limescale in your kettle, you could dry Sentinel X200
http://www.sentinel-solutions.net/product/detail/central-heating/liquids/x200-noise-reducer/

Unlike most cleaners which you put it, clean, then drain out, you put this one in and leave it in. It somehow breaks dows limescale and reduces the noise of bumping, singing and kettling. It is usually about £15 a litre but I saw it at half price in Homebase the other day.

 

[markdon]

Thanks for that, ive been up in the loft, both bottles were left up there.

First is TSSM-4 sludge remover, for established ch systems.
And Sentinel X100 inhibitor.

They any good?