DIY Doctor UK DIY Forums

Could someone help please.

After remedying a problem with the feeder tank going a dry, the back boiler is now firing smoothly again. Result is hot radiators, but tepid DHW.

Investigated the airing cupboard: DHW pipe (going to the coil) is hot after leaving a manual-3way-valve, six inches of horizontal pipe then a 90degree bend to go up to the HW tank opening. Pipe goes lukewarm after the 90degree bend.

Could this be a blockage ? And would a shop bought sludge clearer solve it ?


Also, manual-3way-valve is a white plastic 'simplicity make, and has been seized in the mid way both open position for over 10 years.
Would like to be able to switch between CH & HW. Also this valve is the noisiest part of the whole system.
Can anyone recommend a cheap replacement?

The problem is more likely to be an airlock than sludge.

Thanks for the posting Bob,

I ran the boiler last nite for an hour with all the radiators turned off - that made the DHW pipe going into the hot water tank hot, and whilst the hot tap water was slightly warmer it was still only lukewarm.

Opened up the rads again - rads working fine for about 2 hours - and then no hot rads past the first rad - which is burning hot at the top and cold at the bottom.

What going on ?

Maybe you have a problem with the pump and it is not circulating the water properly. Radiators cold at the bottom are caused by insufficient hot water reaching them.

With the pump off, remove the large screw in the front of the pump (beware a small amount of water will dribble out) and fit a flat screwdriver in the slot in the end of the shaft and see how free the bearings are. It should turn easily. Next, turn the pump on and see how fast the shaft spins.

Thanks for your help again Bob.

Everything is OK now !

Last night I took off the rad nearest the boiler, flushed the rad (no actual 'sludge', more the consistency of ink), also drained a tiny bit of water out of the system via the In rad valve.
Then replaced the rad, fully opened all rads, turned the old faithful baxi bermuda back on at medium temp, balanced all the rads in the property.

Don't know whether it was air, sludge, or what. But the system seems to be circulating well now.

Cheers,