Central Heating making scary sounds

[mr chumleywarner]

I have a central heating system that is making some very strange noises that I’d love someone to explain.

I have a bog standard open vented system with a 5/6yr old Worcester Greenstar boiler, Greenfos Selectric UPS 15-50 pump.
The central heating comes on (HW+CH) and everything sounds normal, then about 5 mins later the pump starts to sound like its struggling, the pipes start banging and then the pump switches off, followed by a scarily loud sound in the pipes that can only be described as wet gravel thrown down a long slide. Everything then stops. A few seconds later the pump starts up again and then stops (this may happen a few times). A few minutes later the system all starts up again and usually is ok for a few hours until its turned off. All the radiators are toasty.


Anybody got any ideas what the sequence of events is and what the sound is. eg why is it intermittent, why does it right itself, what is the gravelly noise, why is the pump struggling.

My guess is that there is “stuff” in the pipes causing some sort of temporary blockage – limescale, rust, sludge? As far as I can guess from forums, it could need a power flush (£££ ), or maybe a few rounds of some Sentinel sludge remover and (gravity?) flush. I'm also guessing changing the pump is not going to fix things in the long term if the pipes are clogged?

I drained the system a few weeks ago to try and remedy this but it made no difference. The noise came back the next day and the day later. It then went away for a week or so and has now come back twice in the last 24hrs. The water coming out of the radiators was relatively clear but the feeder tank in the loft was sludgy brown at the bottom (now cleaned). I don’t think the tank has been cleaned for 8+ years since the system was last drained by a plumber.

any opinions/info appreciated

Mike

 

[Agile]

Greenstar is the name given by Worcester to all their condensing boilers! We need more than that!

Its obviously either a sludge or a pump failure problem.

I don't see how we can be more specific without being there.

Tony

 

[mr chumleywarner]

Sorry, now I'm at home I can tell you its a greenstar Ri installed in 2006 with a power flush done at the same time. It doesn't sound like the boiler but I was hoping someone might be able to shed some light on what mechanically could be going on.

 

[mr chumleywarner]

I finally got round to installing the replacement pump on my noisy system (the noise went away for a while but came back). With the pump replaced, the boiler (Greenstar Ri) no longer works. It has a go but decides not to play ball. What happens when I turn on the CH/HW demand is
* New Pump turns on
* Fan on the boiler turns on
* flame indicator light behind boiler control panel goes on
* Noises happen in the heat exchanger like a helicopter's trying to take off.
* A few seconds later the green light goes off.
* About twenty seconds later the take off noise slows down and stops.
* A few minutes later the fan stops.
* The pump carries on regardless.
* The heat exchanger is hot

The pump is the Grundfos UPS2 15-50/60 Universal Replacement Circulating Pump and its wired up and connected exactly as it's predecessor (Selectric UPS 15/50)
Anyone got any ideas what the problem may be?

 

[yerino]

You have air in your system (airlock) and the boiler is overheating and cutting out.

Have you bled all the radiators, try bleeding the pump and any air bleeds in the airing cupboard.

 

[mr chumleywarner]

I had bled the airing cupboard which had a lot of air in it. The radiators were fine. The pump I'm not sure of how I bleed it I have undone the central silver disc on the pump - nothing came out.
How can I tell if there is actually water pumping - I would expect some gurgling when I turn the isolating valves either side of the pump but nothing much happens noise-wise.

 

[HERTS P&D]

Is the pump the correct way around? are the pump valves open or stuck closed?

Andy

 

[mr chumleywarner]

The pump is in the same orientation as the old pump, the arrow on the body is pointing downwards towards the diverter valve. The top valve has many turns, the bottom is a quarter turn type. I've tried all different combinations. Is there a way of testing the flow - should water come out of the middle screw - my old pump did when I loosened it.

 

[mr chumleywarner]

Water is flowing out of the middle screw now and the pump is getting warm but still no boiler action. Is there a air lock release for the boiler?

 

[ianmcd]

The Ri has an air bleed at the very top of the heat exchanger within the boiler and this MUST be bled you are wasting your time without bleeding this first, it has a short plastic hose on it and be very carefull bleeding this if the water in the boiler is hot as it will spit steam at you

 

[mr chumleywarner]

Thanks everyone for your input. My problem is now fixed

After taking the pump off again and checking the isolating valves, it turns out the bottom valve was sticking halfway and required a little more force than I thought to open fully. With water flowing into the boiler it's happy again.
I'll bleed the system once more just to finish.