My Dad has got an old but fairly reliable central heating boiler, but the rads are getting a bit ropey now, so everytime one springs a leak, I bung in a new one for him.  The rad change is never a problem, but everytime I have to drain the system down, the hot water system packs up.  

Initially I thought the heat exchanger coil thing in the hot water tank was airlocked, so I cracked open the top connection to bleed the air out and sure enough it worked again.  This approach worked OK a few times.

Now things seem to be getting worse.  Last time I changed a rad, all the bleeding on the world wouldn't fix it, so I had to try another approach.  I put a ball valve tee in the expansion pipe in the loft to allow the 'expanded' water to pour back into the header tank.  The idea was that the water would circulate and purge the trapped air from the system.  Anyhow when this didnt work I was advised by the bloke who fitted the system donkeys years ago that the problem was caused by a buildup of sludge.  I put a bottle of that Sentinel 400 stuff in it and hey presto it was OK again about 24 hours later.

Anyhow, yesterday I replaced a seized rad valve, and the hot water packed up AGAIN.  Bummer!  I put the Sentinel 400 in again, and opened the ball valve on the expansion pipe to get the stuff circulating round the system.  The water (?) that came out was certainly dirty but I dont know if that was enough to block anything up.

I dont yet know if the problem is sorted - I am expecting a 'phone call in the morning.

Question is, what is going on here, and if it IS sludge, how can I get rid of it for good?  If it's not sludge what's happening?  Is it an airlock?  ???

Any advice would be much appreciated, as it's starting to p1ss me off!

Windy

You're right about the overhaul Andrew - its certainly due.  I would like to change the whole thing for a new system, but neither myself nor the old boy can afford it at the mo!  

Windy

Draining down 'dodgy' systems is always a nightmare, it can often take longer to drain down and refill than the actual job you were there to do!

That's why we use the large Co2 cylinder and freeze the pipes wherever we can.  

This week I had to break into a one-pipe system to extend it.  Two freeze clips on, within 4 minutes both sections were solid, cut out the middle bit of pipe, valve off each end (for later connection of new rads), fit new section of pipe and all done.

The whole job took about 20 minutes!

It would have taken at least that to drain down!  

And as for refilling, well that could have taken hours with all the rads to bleed.  That's assuming there are no problems................(see Windy Miller post above!).  

I also save the cost on renewing the inhibitor  

Aaahhhh, technology is a wonderful thing  

Email me a set tolook at for starters when I get back rom snooker 8)

scruff

the mind boggles

I want the other bits, like the cylinder connections, motorised valves, pump and the cold feed/ open vent connections.

scruff

It sounds like it needs an air vent on the primary flow top connection to the Hot water cylinder. This is the best way of getting the air from the system. It's not going to sort the entire system out but it is a start!

Is the boiler a long way from the Cylinder?

I've had jobs where it takes forever for the gravity circuit to circulate, it's normally down to air- certainley on the long runs of pipework.

You can always try holding a piece of hosepipe on the ballvalve and letting a bit of mains pressure down the cold feed to try and clear it.

Hope this helps