Noisy central heating with several twists

[qazwsxedc]

I've looked at the Fernox vs Sentinel threads via Google, checked the FAQ, and still not found answers ;-( Can someone enlighten me please?

Background:

4 br house, 12 radiators (one double, 11 single panels). System was drained to fit thermostatic valves a few days ago, refilled, one litre of Sentinel X100 added, and bled.

Still noisy though. Mostly on pump startup, not just when the boiler comes on, so I'm reasonably sure it's air trapped in the system rather than the boiler kettling. In the airing cupboard, where pump feed, return, tank feed and vent pipe meet there's a roughly cylindrical gadget the plumber called a (de)aerator. (In my old house the four just met at an H-shaped bit of pipework.)

The feed to the radiators is via 10mm pipes with odd layouts. There are probably some airlocks in those, and I've tried to force them out by shutting down all but one radiator in turn, then running the pump at full speed. Better, but not perfect.

Questions:

Is one litre of Sentinel X100 enough? The specs I can find say "up to

10 rads", so another canister may be in order. Would accidental overdosing be a problem?

I noticed that apart from its corrosion-inhibiting properties, Fernox MB-1 had the side effect of quietening down the pump, at least in my old house. Does Sentinel have that side effect, too, or was that a red herring?

Are there any other tricks I could try to shift the airlocks? (I don't really want to go round every day for the next four weeks bleeding rads!)

Does the de(aerator) thingy actually do anything useful?

[MikeH]

It says on the X100 container at the end of the paragraph on dose rate that "overdosing does not present a problem", so you're OK bunging a bit extra in. At 1% dose rate a 1 litre bottle is enough for a system containing 100 litres of water (22 gallons). I normally put in a bit more than the standard 1 litre bottle. You don't have to do it very often and the cost isn't significant.

I used one of the cleaning/restoring products in my system before flushing and then adding X100 to a clean fill. The system was quieter afterwards, but I don't know if you could put that down to the X100 or the previous clean-out.

If the noise persists over a period of time and you have bled the system are you sure you that you're not getting air entry into the system somewhere? Pump drawdown maybe or a bad joint somewhere?

Mike

[MikeH]

A couple more thoughts that I forgot to add to my previous post...

Did the system make the same noise before the recent work to fit the thermostatic valves, or is this a new problem?

Have you tried running the system with the boiler switched off to make sure it's circulation noise rather than kettling?

Is the pump speed set where it was originally - maybe it's running unnecessarily fast?

Do you get the same effect when the system is heating just the hot water (i.e. when the central heating is switched off at the timer or via the room stat)?

I've read occasional posts about some sorts of thermostatic valves making a noise if they're not fitted the 'right' way round. From what I remember they were a supposedly bidirectional type that could be fitted in the flow or return, but they tended to make a bit of a noise if they were fitted one way round. Hazy memory, so it may be worth checking on this.

Mike

[qazwsxedc]

Feed and vent pipes do get hot during normal operation so I'm guessing that both remain properly filled while the pump is running. But no, I'm not sure that I don't have an air entry elsewhere except that I can't find any leaks (assuming that a leak big enough to let air in would let water out, too.

Not a new problem, it made the same noise before the new valves were installed.

Yes, I'm sure it isn't kettling noise.

Pump speed is 3 out of 3, also as before - any less and the "far away" rads don't get hot.

No, in DHW only mode it's much quieter.

The ones fitted here are Honeywell VTE117E, supposedly bidirectional. Anyway, the noise was there before the thermostat valves, so we can exclude that.

[MikeH]

That's me pretty well fresh out of ideas and adequate experience.

So... it's not caused by kettling and it wasn't associated with the fitting of the valves and it's predominantly a CH problem rather than DHW....

Has it ever worked properly as far as you know? Switching off rads so that the full pump pressure goes through just one at a time has always cleared air-locks for me. But the combination of 10mm pipework, what you call an "odd layout" and a pump that has to be on full-chat to keep the distant rads warm sounds like that approach may not be enough.

Is the pump up to the job?

Are there places in the pipe layout where it may be worth installing additional bleed valves? I think that's one thing I'd consider if nothing else works.

Mike

[qazwsxedc]

Hah. That's a good one. Quite possibly no. Former owner hadn't even noticed the incorrectly installed room thermostat, never mind the leaking rad valves.

That's what I tried. No luck.

Yes, all rads do get hot eventually. It's just the gurgling that drives me nuts.

Possibly, but I really don't want to go there. The 10mm pipework and the manifolds (if any) are all in the ground floor ceiling / first floor floor or in the walls. And I hate plastering even more than plumbing.

There's got to be an air entry somewhere. But what air entry does not leak water?

[Fred]

Are you able to bleed radiators on a regular basis? Is there one in particular which fills with air?

[roybennet]

I had a problem with air in radiators and upstairs radiator only luke warm. The problem with the upstair radiator was caused by a partial pipe blockage. The pipe was blocked with this strange crud almost like sand. The blockage was where the pipe went up to the vent in the attic and a T connection went off to the upstairs radiator. After the blockage was removed the radiator worked just fine but interestingly air stopped accumulating in the radiators as well.

[MikeH]

Pump drawdown, maybe?

I know you think this isn't the problem because you can feel the vent pipe getting hot, but I think I'd be checking that it's *definitely* not a problem, especially as you have to run your pump at full speed. Maybe there are circumstances under which air occasionally gets sucked into the system - enough to cause your symptoms.

Mike

[qazwsxedc]

Bingo. In a way. The pump created just about enough head for the vent pipe to, well, vent into the header tank. Between tiny trickle with all rad valves open and decent flow (!) with some closed. Along the

5-inch fall and resulting turbulence the water picked up enough dissolved air to create a problem. At least that's my theory. Solution: Turn down the pump one notch and rebalance yet again.

Been like that for 24 hours now, bled rads once in the meantime. All quiet.

Mike, have a cold one on me.

[MikeH]

Very good of you, thanks! As it happens I am doing just that 'as we speak'. So - here's hoping it's a permanent solution. You certainly don't want that level of pump-over. In fact you don't want any pump-over at all. It will, as you say, aerate the water and add to the potential for system corrosion.

If, after rebalancing, your distant rads don't get properly warm with the lower pump speed, you might need to look at the geometry of the pipework around the pump and vent-pipe connection.

Mike