CH system really upset since new rad fitted and drained-refilled

[sololite]

Our CH system is really upset since we replaced a radiator a couple of months ago and neither my plumber or British Gas can fathom the cause. I am hoping someone might have some advice for me because it is really testing my sanity.

Our CH system is open vented and has been fine for 9 years since British Gas put a new condensing boiler in.

Two months ago, a plumber replaced an old rad for us and I drained down, put in system cleaner, drained down again and refilled with inhibitor.

The boiler then started clanking and shutting down but would sometimes run for several days without a peep. I spent next few weeks bleeding everything and trying to work out the cause, I also put in X400 for 3 weeks and drained down/refilled again with no effect, eventually admitting defeat and calling British Gas in.

They replaced the pump which they said was faulty and things improved for a while but then the clanking returned. They then came back and said the heat exchanger should be replaced and it was probably sludge or damaged. As this was going to be a few hundred quid and they couldn't guarantee it would solve the problem or reimburse me if it didn't I decided to roll up my sleeves and see if I could prove/disprove my theory that air is somehow getting into the system and causing our woes.

I am trying to rule things out one by one. I have got it to stop clanking by not running the HW circuit at the same time as the CH and by bleeding air out of couple of items frequently during the day and turning the pump down to 2.

So the clanking has gone but now I am bleeding a tall column radiator downstairs constantly and the mag filter next to the pump. It is only this one rad that has any air in it and the mag filter will release air for a few seconds every time I bleed it.

Other things I have noticed are: once I saw steam coming off the overflow tank, once I saw hot water going from the vent pipe into the overflow tank and a couple of times I have noticed a couple of bubbles on the surface of the overflow tank.

British Gas say they are seeing nothing untoward in the pipe layout and given they did a lot of it and its been running smoothly for 9 years makes me think its not faulty piping.

I've googled and read about micro leaks - is there away to find them? Is hydrogen a possibility or is the fact that we've done a system flush twice now make it unlikely?

I am stumped but feel I am gradually getting closer, I am hoping some experienced person might provide the breakthrough I need to stop me prowling around in the dead of night listening to gurgles or up and down the loft ladder like a yoyo.

thanks for any assistance

regards,

sololite

 

[jeff the gasman]

Bet there's magnetite blocking the flow where the cold feed joins it.

 

[sololite]

Hi Jeff. That réponse was in world record time - thank you.

I asked the British Gas engineer if there could be something blocking the 15mm cold feed where it joins the 22mm vent pipe and he was a bit dismissive telling me I wouldn't have been able to refill after the draining downs if it was. He also spent some time on that joint with a long stick with a magnet on it before Christmas, so I wonder if he was suspicious of it.

As part of my drain down the first time I cleared all the muck out of the overflow tank and wonder if some of the yucky algae sludge stuff went down it.

I've attached a pic of the 15mm feed joint, it does a couple of right angles before it heads northwards into the tank in the loft about 6ft away.

Is there anything I can do to force water through it in attempt to dislodge it? I really don't want to get my spanners out and start fiddling but I guess will have to if I need to.

thanks for taking the time to give me some advice.

regards,

sololite

 

[jeff the gasman]

N

Hi Jeff. That réponse was in world record time - thank you.

I asked the British Gas engineer if there could be something blocking the 15mm cold feed where it joins the 22mm vent pipe and he was a bit dismissive telling me I wouldn't have been able to refill after the draining downs if it was. He also spent some time on that joint with a long stick with a magnet on it before Christmas, so I wonder if he was suspicious of it.

As part of my drain down the first time I cleared all the muck out of the overflow tank and wonder if some of the yucky algae sludge stuff went down it.

I've attached a pic of the 15mm feed joint, it does a couple of right angles before it heads northwards into the tank in the loft about 6ft away.

Is there anything I can do to force water through it in attempt to dislodge it? I really don't want to get my spanners out and start fiddling but I guess will have to if I need to.

thanks for taking the time to give me some advice.

regards,

sololite

no, needs cutting out and replacing. Convert to combined vent and feed too.