Very Loud CH Problem

[GJS]

I've a problem with the CH in my house that I moved into five months ago - so not much history on the system. It is open vented, fully pumped Y-Plan, with an Ideal Standard NF50 boiler, 11 rads, HW storage tank.

When I moved in the rads were only heating up at erratic times and the HW was RED hot regardless of tank stat setting. I traced this to the zone valve actuator, replaced it, problem solved. I also fitted a Honeywell CM907 room stat to replace the existing cheapo unit. I've got one small rad removed at the moment and one turned off at the rad valve in rooms that I'm decorating. When I took the one rad off I remember it struck me as having a lot of black sludge in it. I've noticed that there is generally a lot of air in the system which accumulates in the bathroom rad which I bleed at least once a week with loads of air coming out.

The problem: About a month ago, the heating turned on at the programed time (from cold) and there was a loud banging noise a bit like someone kicking a tin can down the road. After about 30 secs there was a gush of water from the header tank overflow, loads, at least a whole tank full I would say. The system then ran normally. As a result of this I turned the pump speed down from 3 to 2 thinking that the problem might be "pumping over". This Sunday the system turned on at 7am and the tin can noise started up followed by the gush from the overflow and then followed by some really loud cracking and banging noises. I mean REALLY loud. After they stopped there was loads of gurgling noises coming from the rads for about an hour. Then everything was back to normal.

I've checked the layout of the system as best I can (pump position in particular) and it seems OK to me. I've yet to look inside the header tank. I don't know if removing the one rad and turning off the other has started this problem as I haven't been in the house long enough to know if it was happening before. It might have happened lots of times when I've not been in. I've done some other plumbing round the house but all on the water side, not heating (fitting a new bathroom, shower pump, essex flange etc)

Any ideas? I suspect maybe a blockage somewhere?

All advice gratefully received.

Cheers.

 

[Slugbabydotcom]

3 Ideas

1. Your system is full of sludge and this now needs sorting. Best way of doing that is with a powerflushing machine and full chemical treatment. Cleanser and inhibitor.

2. Your pump has probably been killed off by the sludge.

3. I have seen geysers like this caused by a blocked feed pipe so if you sort out the other 2 and you still have a problem especially with refilling the system then sorting this out is your next move.

 

[GJS]

Thanks for your reply slugbabydotcom. I had pretty much come to the conclusion that I have tons of sludge and one or more blockages. Do you think it's worth doing a conventional flush first, as a powerflusher seems to be hard to get hold of? I've got good mains pressure so I was also thinking of putting that into the system as a half-way-house.

I've got no other heat sources in the house so this might have to wait 'till the spring.

Another question; when everything else is sorted, how do I determine the correct pump speed?

Thanks.

 

[Slugbabydotcom]

Any flush is better than no flush at all. I think your immediate problem is that the pump is sticking. If you renew the pump without flushing then you will shorten its lifespan.

A suggested compromise:-
Do as much of the following as you are able.
Flush the sytem as best you can.
Take as many rads off the wall as you deem feasible Starting with biggest downstairs rads and flush them through with a hosepipe.
With the rad off the wall connect a hose to each rad valve and flush some water through.
Renew the pump
Fit a magnaclean or boiler buddy.
On page 2 of the FAQ's theres a wicked cheat [24] to get water into your system if your system wont refill due to a blocked feed pipe. I find that this method has a good success rate in clearing partial blockages and about 1 in 6 of total blockages.

Pump speed:-
As low as you can get it without causing the boiler to kettle and yet provide sufficient hot water to all the rads.

With only 3 settings its hard sometimes to find a balance between pumping over and kettling.

Leaving it to pump over could cause one of those 'naughty immersion heater type' situations where the tank water gets hot and splits causing boiling water to pour through a ceiling as in the recently publicised case. To balance this point I will say that there would only be a couple of gallons of boiling hot water at most in a feed and expansion tank and this is a lot less likely to be fatal than the 20+ gallons found in a hot water storage cistern.
Kettling could cause damage to your boiler and system although it can sound scary it is usually the lesser of the two evils from a safety point of view in my opinion.

 

[namsag]

Is there any other name on the boiler , As it may be a pump over run stat problem.
Some of these work by sensing heat within the boiler casing , what happens is after heating turns off stat does not reset properly so that it does not come on when there is a new demand on boiler so boiler fires up and because pump does not come on water turns to steam and bangs and clatters through system out of vent, then the stat senses heat within boiler and brings pump on which would explain why your system then runs ok for hours/days.
It may even just be the pump sticking and as the heated water bangs through system it is enough to kick start impellor