Odd noise from the heating pump.

twopenny

My heating used to work fine until I started to replace bits, clean etc. So rads flushed, new timer, new TRVs, new actuator. 20yr old system only been used for 6yrs.

Had banging in the pipes in the loft when it had been on for several hours last winter, not when I put it on the 1hr booster.

3 gas people came and checked everything and couldn't find anything wrong.

This autumn Heating engineer came and tested all parts working fine. He set the pump to shut off in 8mins rather than 15mins.

Now the weird thing.

The pump working heating on it's own starts off fine purring along. After an hour or so it gets really noisy.

Plasterboard small bungalow this echoes in all rooms and drives me nuts.

However it is beautifully quiet if the hot water is on as well. (immersion). But I can't have both on all the time. No problem with pump noise when heating water only.

On the plus side I seem to have lost the knocking noise in the loft  Though it's not been on long yet.

Any ideas I'd be grateful.

ThisIsWeird

twopenny said:

2) He set the pump to shut off in 8mins rather than 15mins.

1)Now the weird thing.

However it is beautifully quiet if the hot water is on as well. (immersion). But I can't have both on all the time. No problem with pump noise when heating water only.

That suggests the pump is finding your system restrictive, and that would typically occur when many of your rads have shut themselves down - say via their TRVs.

The pathway to your hot cylinder is peasy, and the fact the pump goes super-quiet then adds to this likely cause.

Solution? I guess make sure you do have a by-pass rad - ie one that's always partially open and doesn't have a TRV fitted. Mind you, a modern boiler should have a built-in by-pass.

But, I suspect the ultimate solution would be a Smart pump, which will adjust to suit demand; if the system becomes restrictive, it'll back right down.

Re (2) - how did he set this?

twopenny

That makes a lot of sense.

The radiators do heat to boiling then stop to barely warm at the top but the house seems warm enough. Of course it's not really cold enough to test.

It didn't used to do this before the noises in the roof or a lot of people poking around.

How do I have do a by pass rad?

Would that radiator just get very hot?

Re (2) no idea. I think it was on the pump itself. He's a good guy.

And I've had different ideas that cost money from several. He reckoned nothing was obviously wrong and I didn't need all the stuff recommended.

vacheron

It sounds like the system could be kettling, this would occur when the water in the boiler is boiling (despite the name a modern boiler should never "boil" the water). This could be because the water is passing too slowly through the combusion chamber due to lack of flow, or because it is already too warm when entering the chamber (such as when the radiators have been running for a while, like the hour or so you mentioned), meaning the additional heat being added to the water is tipping it over boiling point, bubbles from which could then rise up into the loft pipes. 

This shouldn't happen for more than a few tens of seconds though, because the boiler has an overtemperature stat on the water exiting the chamber, and this will activate and cause the boiler to shut off until it cools down. This "boiler cycling" is also undesirable and will cause the house to take a long time to warm up.

Things to try. 

• If you have thermostatic valves, note their postion then turn them all to maximum, see if this solves the problem. If it does, the valves could be shutting off too many radiators before your thermostat reaches the desired temperature.

• If you have a central heating pump with variable speed settings, turn it up a notch and see if that reduces the problem. (It may increase the constant pump noise, but may reduce the sudden pipe noise after running for a while). 

twopenny

Interesting. Sounds plausible.
I won't know about the pipes in the loft till it gets cold. Can't get up there myself at the mo due to trapped nerve.
He did reset the temperature on the boiler as well.

I have done all the turning up, down on the radiators before and it didn't really have any effect.

I will ask him back when the heating is running but needed a few suggestions first.

I've already had the 'you need a new pump & airlock valves' or 'you need a thermostat on the wall' from a couple of engineers when the others have rejected the idea. 
So I'm in need of some defence.


I won't try fiddling with the pump. I'd rather he didn't have to undo anything not done by him. 

ThisIsWeird

Photo and make/model of boiler, please? And ditto of pump.

twopenny

Both camera batteries flat so to be resumed.
An interesting thing to try is when it's making the sound of an aeroplane cabin would be to open the valves and see if rads get hot and noise reduces.
At the moment in the south west it's 19c and I've been in the sea so I'll pause if that's ok.

ThisIsWeird

twopenny said:

At the moment in the south west it's 19c and I've been in the sea so I'll pause if that's ok.

Well, that's a lousy excuse!

Yup - quite a balmy day in the SW, isn't it

Ectophile

A bypass radiator is one that doesn't have a TRV fitted, just the old-fashioned tap at the end.  It should always get hot when the heating is on.  Don't turn that one off.

Alternatively, the plumber can fit a valve to let water bypass the whole heating system if the pressure gets too high.

twopenny

Thank you Ectophile.

7 rads, 3 tinywiney, 4 a bit bigger. Small pipes.

The thing is that it was running fine until I started replacing stuff. Flushed system - new immersion -

The TRVs was a rush case of 'these were the nearest I could get' and screwed on.

The new actuator was when this started (only guy who I'm doubtful of) - but others have looked and said it's ok.

Sorry not the best but standing on tiptoe with head in cupboard!

ThisIsWeird

So it's a 'heat only' Baxi boiler, with its output set to just over '3' out of '6'. And this gets the rads up to temp with no issues? Cool - in which case I'd try lowering that output a tad, just to reduce the overall water temp being generated by the boiler.

Of course, if it then gets too low to heat the rads properly, it'll need turning up again!

That's a frost 'stat in your second pic - I presume it's in the same room as the boiler, and this is an outhouse of some sort - the garage, perhaps? That's all fine.

The pump looks like a typical Grundfos, I presume a manual type with three fixed speeds. That's usually ok too - it's what you'll find in the majority of installations. 

I'm not a plumber, so these are just 'thoughts';

I suspect that when you replace the boiler, things will be fine. More modern boilers will likely have an effective by-pass system built in, and will certainly have better flow temp control - ie the boiler shouldn't ever find itself in hot water (brrrr-cheesh.)

When it comes to a new boiler, I would also personally consider going 'system', as it loses the F&E tank, and everything is built in, including the pump. So I'd imagine even better water control, including - I imagine - a variable-speed pump.

Meanwhile, what to do? Well, ideally, you want to know the cause - and then fix that. But there's two things that could help to sort it, but whether it's worth doing requires a proper plumber to decide. One is a variable-speed pump - a 'Smart' jobbie. These adjust their speeds according to demand, so no more trying to force excess water through the remaining open rad. I remember when I first fitted one of these for someone, I couldn't believe how quiet it was, and was tickled by the stupidly low power consumption for most of the time - 15 watts or something. And the other thing that would make me more happy in an older system is an auto by-pass valve. These will open and allow a by-pass flow only when required, so they won't steal any flow when radiator demand is high. But as rads begin to shut off, and the flow becomes more restricted, the valve will open enough to allow the water to keep circulating.

But, you need your own plumber to advise on these.