Blocked pipe, banging boiler, now nothing..

Hi all,

What a time for the CH to pack up..-5 outside

Have a GlowWorm Ultimate 120, vented system and a nearly new pump. Recently had a blocked feed pipe to one of the downstairs rads. Not the end of the world and lived with it.

Yesterday, the boiler started playing up. It would fire up fine, stay lit for about a minute and then would start banging - best description is that its similar to the sound made by a manual pilot light switch on a patio heater. The banging seems to be centered around the flow pipe to the boiler where it enters the cast iron tank. About 5 seconds after the banging starts, the boiler shuts down.

Trying to kill a couple of birds with one stone, I drained the system completely and cut out the section of blocked pipe. It was scale / rust which had formed a plug in a 15mm elbow where it spurred off the 22mm main pipe.

Anyway, filled the system, bleeding rads as I went and added a decent dose of Furnox cleaner into the expansion tank.

The boiler noise and cutting out still happens . To start with, the downstairs rads were heating up but upstairs were barely luke warm. Now every rad in the house is stone cold.

The pump seems fine. Header tank is full (and steaming ??). The downstairs rads are air free - upstairs rads keep getting air in and there doesn't seem to be enough pressure to either fill the rads or even flush the air out...

Apologies for a long winded post and thanks muchly for any suggestions for a next step forward...

Normally would always suspect the pump with the banging and early cut out. Would still be suspicious despite you saying seems OK. Alternatively if system prone to blockage, slow to make up and little pressure to clear air, sounds like cold feed between header tank and make up point to system has a blockage. Either renew or try backflush. Check out Pump first.

Fair bet the pump's full of clag. Rust sticks to the brass valves too.

Thanks chaps..I agree that the symptoms do suggest the pump could be at fault but it was fitted new just 6 weeks or so ago. The previous pump (already in place when we bought the house) was of a lowish flow rate for the number of rads we have. Replaced it with a higher capacity pump to try and improve circulation and it made things worse

Also, I split the pump yesterday to check that it wasn't full of muck and that it was rotating freely - yes on both counts..

In light of your suspicions though, I'll re-check the pump later today...

There has been some improvement overnight, apart from the boiler's overheat sensor tripping in the night - indicative of poor flow around the system, I presume. That was at the time when none of the rads were warming up..

Now, at least the boiler has stopped banging . It still only runs for a minute or so before cutting out but I guess that's down to poor flow again. Flow to the upstairs rads is still pathetic. For rads closest to the boiler, it can take 5 minutes for air to meekly escape and still the rad only gets warm at the bottom. Rads farthest from the boiler show no sign of life yet - well, apart from gurgling away all night.

The system is Furnox'd at the moment so it will need a drain down soon. I was hoping to get improved flow to all of the rads such that the whole system is cleansed but I am doubtful that this is going to happen.

So, are there any pointers to refilling the system after a draindown to avoid airlocks ? ie. all rads turned off and then turned on one by one and bled at the same time, starting downstairs ?

Thanks again for any suggestions, I'm on a steep learning curve here !

Check the new pump has been installed in the correct flow direction

If the header tank is still steaming this indicated probable pumping over, report back if it is as there are a lot of possibilities as to why.

With a 120,000 btu/hr boiler you have a system at the limit of a standard domestic (15/50 or 15/60) pump, therefore it should be in tip-top condition to cope with your loads. Check it is as clean as a whistle when you drain down as your previous posts suggest lots of c**p in the system. Remember, the better it pumps, the more c**p goes through it

Don't take short-cuts on the flushing, and consider doing the same again in the spring as you WILL have deposits in the boiler which will only shift after the flow rate is increased, catch 22 but perseverance will pay.

meldrew's_mate said:

Check the new pump has been installed in the correct flow direction

Click to expand...

I fitted the new pump and installed it in the same flow direction as the previous unit. That's not to say that the old pump was fitted correctly but I believe that was fitted by a 'proper' plumber as the previous occupants were not the type who would do anything themselves Also, we had the system serviced just over a year ago and nothing was flagged by the engineer.

meldrew's_mate said:

If the header tank is still steaming this indicated probable pumping over, report back if it is as there are a lot of possibilities as to why.

Click to expand...

It certainly was last night - I didn't get a chance to check this morning...Any 'obvious' possibilities I could check for ??

meldrew's_mate said:

With a 120,000 btu/hr boiler you have a system at the limit of a standard domestic (15/50 or 15/60) pump, therefore it should be in tip-top condition to cope with your loads.

Click to expand...

A big house with 14 double and 1 single radiators..

meldrew's_mate said:

Check it is as clean as a whistle when you drain down as your previous posts suggest lots of c**p in the system. Remember, the better it pumps, the more c**p goes through it
Don't take short-cuts on the flushing, and consider doing the same again in the spring as you WILL have deposits in the boiler which will only shift after the flow rate is increased, catch 22 but perseverance will pay.

Click to expand...

Judging from the bits and pieces of scale / rust in the 22mm pipe either side of the blocked 15mm spur yesterday, I suspect there may well be more in the system.. Save PowerFlushing the system, is there anymore I can do to achieve a decent flush out ?? Rad valves off and use of hosepipes and mains water pressures ??

You seem to immagine that you can have a seriously sludged system and just cut out a bit of pipe and shove in a chemical and all will be fine!

The reality of the situation is that your system has all the symptoms of serious blockages. You have put an undefined product in which may be totally unsuitable for the problem.

Some chemicals will loosen bits which then move and cause blockages like pump valves or pump inlets. It sounds as if that may be part of your problem.

The correct solution would be a power flush using the appropriate chemicals to treat your system.

Tony Glazier

Agile said:

You seem to immagine that you can have a seriously sludged system and just cut out a bit of pipe and shove in a chemical and all will be fine!

Click to expand...

Not at all, Tony.. The rest of the system has been OK. Whilst a couple of the other rads were not as hot as I suspect they should be, it was just one which was stone cold. I traced the blockage to an elbow in the 15mm feed to the rad, cut out an 18" length of the 22mm main pipe from which it spurred, shifted the blockage and re-fitted it with compression joints.

With the system drained down, it seemed like the ideal opportunity to flush through with Fernox Heavy Duty Cleanser.

Agile said:

The reality of the situation is that your system has all the symptoms of serious blockages. You have put an undefined product in which may be totally unsuitable for the problem.

Some chemicals will loosen bits which then move and cause blockages like pump valves or pump inlets. It sounds as if that may be part of your problem.

The correct solution would be a power flush using the appropriate chemicals to treat your system.

Click to expand...

Powerflushing the system is a probable next step - I admit I didn't like the look of some of the flakes that came out of the blocked pipe. As you rightly pointed out, the system could be full of that kind of crap and its formed a plug elsewhere in the system. I just wanted to make sure I wasn't overlooking something glaringly obvious with the clanking boiler and poor circulation.

Further to last post, the boiler has stopped banging completely and the amount of air being bled from the rads is getting less - albeit very slowly...A few of the upstairs rads are even starting to warm up....

A couple of quickies if poss.

1) I had a quote of £300 for a complete PowerFlush. That includes all the chemicals, a plumber and his mate etc. For 15 or so rads, that sounds like a pretty good price to me. Am I correct ?

2) Poking around and checking the pump last night, I noticed that the Honeywell Motorised Diverter Valve (2 port) on the HW circuit has failed in the open position. This was verified by removing the cover and watching the cog drives when the HW is switched ON / OFF at the programmer. It doesn't even twitch... Also, the manual slider on the top of the valve doesn't seem to be connected to anything at all - there is absolutely zero resistance when its moved from side to side.

Could a failed diverter valve on the HW circuit explain the short cycling of the boiler ? On for a minute, off for minute, on for a minute etc... Which might then explain why the CH is not getting to full temperature...

Yoda, £300 for a powerflush is about right. I charge £295 + VAT all inclusive of chemicals. For 15 rads, it'll take about 6 - 7 hours to completely flush out.

Cheers, Richard
www.agoodplumber.co.uk

saviller said:

Cheers, Richard
www.agoodplumber.co.uk

Click to expand...

Is that allowed?

NB
www.absolute-rubbish.co.uk

Apologies if contravening forum rules - first post - will not include in future