Central Heating Problem

Groping around in the dark - is there any difference in the noise between CH only and HW only?

No

http://www.plumbingpages.com/featurepages/WaterProblem.cfm

"Being a direct result of increased temperature, lime scale will form in the hottest part of the system, usually the heat transfer surface in the boiler. In contrast, iron oxide first forms as a sludge at the point of corrosion and will only become a scale if carried by the water to the heat exchanger where it can become hardened by baking"

It's possible that you've moved the sludge in the rads and redeposited it in the heat exchanger.

Perhaps a boiler only clean might help.
http://www.plumbingpages.com/featurepages/HWscalehome.cfm

"Allow this to circulate for 24 hours at 700C" ...I'd drop the temperature a tad ..

what make of boiler is it? is the thermostat cutting down to late causing kettling in the boiler?

does the boiler have a modulating gas valve or just straight on-off control?

can you describe the noise eg whine or banging

will pop back later and see if I can help

Pete

Thanks Pete

It's an Ideal Minimiser SE50 (condensing).

I don't think it's the control-stat. It was OK before I did this misguided operation. Noise is less at lower setting as you'd expect, but if too low it won't reach the DHW stat set temp (tho I'm using the immersion heater till this problem cured). Again, it was OK before.

Straight on-off control.

I'd describe the noise as between a whine and a howl. No banging.

Also I've started a test with steel nails in a jar of system water. Still OK (24 hours in). The system water has just a slight cloud (unchanged). The controls in tap water are already rusty. Slightly reassuring that if I do replace the h/ex it will be OK (apart from the £££!)

Cheers.........Codey

Maybe you should check the water circulating pump in your system. Find it and listen to it to make sure that the noise is not coming from it.

Changing the setting on the Heat Thermostat only puts the boiler OFF /ON, but I don't think it should affect the noise in the circulating pipes and radiators if these do not have thermostats that reduce the flow in them (?).

If you have individual thermostatic valves on the radiators, then closing them partially and reducing the noise will indicate that you have dislodged particules that hav found a way to block somewhere the flow.

More details on the installation are required...

what kind of sound?

like a whistle, scratching, water hammer, like water spraying, or pop and where it occurs?

if you are assuming particles in the heat exchanger, did you check any leaks in your heat exchanger? direct contact of hot and cold will create a thunder like sound. leaking steam valve can make sound too. defective relief valve will pop always. trap water in the steam line can create water hammer.

Thanks Erlo, but see #5 for noise.

check the feedwater control valve and feedwater line inside the boiler.

whining sound could the fwv is leaking or not closing proper. check also steam non-return valve for the same reason. Sometimes you need only clean the deposit (scale) that prevet the proper closing and openning in it. i assume the sound you hear is in the boiler.

Thanks everybody for recent posts. To answer the points :-

Boiler make - see #5

System is open vented. Was a galvanised steel f & e tank pretty rusty so replaced with plastic in last few weeks.

I don't think it's the pump, the noise doesn't start till the circuit water gets hot, 5 - 10 mins after boiler start.

Today I tried to remove the heat exchanger, to have a go at cleaning it and if no cure to fit a new one. It's difficult to work on, but there is no way it will ever come out without destroying the boiler.

The instructions on the X400 can say circulate hot for minimum 2 hours, but for heavily sludged systems longer, up to 4 weeks! Wasn't heavily sludged, no rad cold spots so I gave it 20 hours hot. There is no warning to say that if insufficient time is given there is a danger of causing a worse problem than the original one due to solids being deposited in the boiler. Nor is there an indication how you can tell that enough cleaning time has been given. So I'm not impressed by them. I phoned them and they said I had not circulated the X400 long enough. They said I should clean the system again, with their X800.

I don't fancy going through a complete clean again for a number of reasons, one being I wouldn't be at all sure it would cure it. But I've had another idea - just put the X800 through the boiler and hot water cylinder. I've got valves on the common flow and returns for the rads so easy to arrange, and fairly straightforward to flush out after.

If that doesn't work it looks like a new boiler.

Cheers........Codey

Hi Codemaster,

I concur with your feelings about the 'brew', I ran it both cold and hot and the end result was dismal!.When I removed each and every rad, took it outside and blasted it with my Karcher the black crud came out for several minutes. I also did not have any cold rads so I felt that the stuff was not up to the task. As I live in a soft water district I knew that scale was not going to be an issue just the black ferric crud.

Your old galv F&E tank was not helping matters when it became a raw iron surface etc, so some of the ferrous/ferric material now in circulation would have been derived from that source.

Next I did as you think using a very short circuit to the DHW coil with all rads zoned off. Things improved but the boiler still sounded too musical for my liking.

I upgraded the pump to a Grundfos 15/50 and included a pressure differential valve to allow recirculation, as the increased output would not be realised when the TRVs started to close down.

I also added Fernox MB-1 solution to the whole thing and since these jobs were done it has been as quiet as the proverbial church mouse.

I have used Fernox solutions professionally for many years and it seems to do the best job at a realistic price,homoeopathic boiler remedies don't work either!

My only other comment would be to have a close examination of the fire-side of the main heat exchanger to see whether there is any indication of uneven flame patterning as a partly obstructed burner diffuser can cause excessive localised heat output with the attendant overheating and noise generation. I wouldn't rule out anything at this stage as it appears as you have had a number of years of trouble free operation prior to this issue arising.

Hopefully you can avoid taking that final step of junking your faithfull thermal friend in lieu of something which will most certainly last less long.

Best wishes,

Massey.

You have done every thing by the book. The question that I have, is did you replace the cushion/ expansion tank when you did the boiler?

Hi Codemaster,

What make of boiler is it? Most of them are sensitive to fouling of the heat exchanger surfaces and the noise you are hearing is 'kettling' or localised overheating due to a reduction in the rate of heat transference across the heat exchanger. You might also suspect the performance of your pump which may well be worn.

As you have had quite a number of years of trouble free operation it does sound like a case of impoverished flow.

I am not a great believer in the efficacy of these wonder treatments in terms of their performance on heavily fouled older installations. You may have to take the heat exchanger out and use a pressure washer to ,blast the crud out'.

Best wishes ,

Massey.

Sound like you have some good ideas. However, I have to ask whether you might have air in the system, whether you have auto vents or manual vents to get the air out at the high point?

I had the same problem after replacing the hot water cylinder which entailed a bit of pipework alteration, the 'banging' in the boiler appeared a couple of minutes after every start up and gradually quietened down after a couple of minutes.

I tried all the obvious fixes, even reversed the pump flow to no avail. The answer happened completely by accident - we put in a new bathroom which had a modern chrome plated tubular radiator which was a lot higher on the wall than the old radiator. After fitting the new radiator we had no more boiler noise!

My conclusions are:

1. The head water supply to the boiler had a slight 'uphill' slope on a small section of pipe which must have reduced the actual head water pressure at the boiler and it was causing low pressure pockets of boiling at the heating surface. Raising the radiator raised the water level in the whole system by less than a meter but it was enough to stop the banging noise in the boiler.

2. The pump was possibly cavitating and this disturbance was also affecting the flow inside the boiler.

Try altering the pipework from your header tank to give a better head of water at the boiler or move the pump further away from the boiler.