Pipes making a racket when boiler starts heating the water

fraggleKFC_2

Hi, I am aware there are several threads on this but none of them have a solution to my problem.

When my boiler kicks in for the hot water there is around 20 seconds of pipes banging and clattering. Then seems ok then happens again 20 mins later. This happens both times water is scheduled to be heated, ie 6am, 4pm.

When the central heating kicks in there is no problem.

I have bled all radiators frequently, bled the hot water side of things where I can, ie taking the top off the automatic air vent and letting water gurgle out for a while but no change with the problem.

What I am thinking now is that last time I drained the system to replace a radiator valve I may not have drained the hot water side of the system, ie tomorrow i will drain system as normal, then take the top off the AAV and hopefully watch more water drain away. then refill whole system and hopefully problem resolved

Does anyone have experience of this and any idea if it is the right thing to do?

Thanks

Fraggle

keystone

You haven't said but I'm assuming its an open vented system?

Cheers

fraggleKFC_2

Yes, open vented

keystone

Sounds like you may have air in your coil. If so it can be a b.gger to get out but persevere and you will.

Cheers

nikanika0

we have exactly the same thing OP, plumber stopped by, he has fixed it, but the noise came back again. Can't be bothered any more. We got used to it I think.

southcoastrgi

nikanika0 wrote: »

we have exactly the same thing OP, plumber stopped by, he has fixed it, but the noise came back again. Can't be bothered any more. We got used to it I think.

get a decent plumber

fraggleKFC_2

Drained and refilled whole system, problem still exists

10 minutes after the hot water starts heating there is banging in the pipes, specifically 2 radiators near the boiler. the radiators heat up slightly. I bleed the radiators till just water comes out, 10 minutes after the pipes banging if i bleed radiators again i get alot of air coming out. This is all with the heating off!

Also, whilst the water is heating, one time I went into the loft to the expansion tank. After the banging, the tank started to fill up with roasting hot water coming into the tank via the pipe at bottom of tank. Water level raised around 2 inches. 30 seconds later water level back to normal with water going back down the pipe it had just come up!

Anyone any idea whats going on there???

Thanks

southcoastrgi

air lock or blockage

keystone

The system balance is clearly seriously on the bonk and as SCRGI says that says airlock somewhere or blockage somewhere. The problem is tracking it down which is going to be quite time consuming remotely.

Which tank is backfilling with hot? Is it the main cold water tank or is it the smaller feed and expansion tank? I can't be 100% certain from your post.

Does the backfilling also occur when the system is off?

Which tank is higher in the roof?

If its the big 'un it backfilling with hot water it could be that the coil has failed in the cylinder. It could also be something as simple as mains cold crossing over into the hot at the kitchen mixer or at shower valve.

If its the small one what is the configuration? It should be boiler, pump, feed vent and no more than 150mm between feed and vent.

The prodigious amount of air you are getting implies that air is being sucked in via the vent pipe. With system cold, hold a small glass of water under the open end of the vent and get someone to turn the boiler on. If the water level in the glass drops you know that air is being drawn in.

However, the fact that hot water is coming back up the feedpipe suggests that the vent might be physically blocked or airlocked but if it is then it won't be drawing in vast amounts of air.

Tried turning the pump down to see what happens?

Too many possibilities. Time to bite the bullet and someone in.

Cheers

fraggleKFC_2

Thinking that there is a chance this may be caused by faulty 3 way motorized valve, its a danfoss hsa3. The radiators near the boiler do get slightly warm when only hot water should be on.

Is there and way to check this without removing the valve? Is it easy to replace the valve? Is it just a case of buying one, fitting it to pipework where old one was-are they a standard connection?

Anyone recommend a good one?

Thanks

southcoastrgi

sounds to me like the pump isn't switching on when only hot water is calling, have you checked that's it running on hot water only ?