Vented system, rads struggling to heat, scolding hot water??

[BinM]

I'm after a little advice please.

I have a simple heating system in my house which has a back-boiler, pump and timer. Both the hot water and central heating are vented (2 header tanks in loft) and it is a dual pipe system (flow and return). There are 11 radiators throughout the house and a hot water cylinder in the airing cupboard.

My problem is that no matter how much time I spend balancing the system it's impossible to get a decent amount of heat out of all of the radiators.

Hot water supply is good and the temperature is very high.

Please can somebody tell me how the hot water cylinder is connected to the system? I can't easily tell because all of the pipework is under the floor boards. Is it simply connected across the flow and return like a radiator? If so could this be the reason that I can't balance the system out properly? There is what looks like a thermostatic valve connected in line with the pipework to the coil in the cylinder but it's seen better days and is pretty good and seized.

Also as a second question does anybody know when speeds 1 and 3 would be used on the central heating pump? Mine is set on 2 just like everybody else's I've ever know?

Any advise would be greatly received.

 

[stem]

Sound like this is similar to what you have, with the exception of the boiler type.

Untitled

• stem
• 11 Jan 2010
• 4

The water from the boiler flows by gravity (hot water rises cooler water falls) around the hot water cylinder, which if the thermostat is broken will eventually get as hot (or very close to) as the water in the boiler because the process is uncontrolled. If the pipes from the boiler to the cylinder are not insulated this heat will be being replaced continuously.

The radiators are fed by the pump. Have they ever worked properly? If not you could have a bad system or piping design.

If has has worked OK at sometime that would suggest something has changed. If you have tried balancing the radiators and it hasn't worked, maybe they are full of sludge. Is there corrosion inhibitor in the system? You could always remove one radiator and wash it out, if it's full of sludge the system will be ready for a clean.

If the radiators are just cold at the top, maybe they need bleeding.

Try the pump on speed 3 see if it makes any difference. 11 is a fair few radiators. It will probably use a bit more electricity and be noisier.

 

[JohnD]

Please can somebody tell me how the hot water cylinder is connected to the system? I can't easily tell because all of the pipework is under the floor boards. Is it simply connected across the flow and return like a radiator? If so could this be the reason that I can't balance the system out properly? There is what looks like a thermostatic valve connected in line with the pipework to the coil in the cylinder but it's seen better days and is pretty good and seized.

photos please

//www.diynot.com/forums/viewtopic.php?t=129539

and of the pump and the pipes around it

when you bleed the highest radiators in the house, does water squirt out forcefully, and keep squirting without loss of pressure?

no matter how much time I spend balancing the system it's impossible to get a decent amount of heat out of all of the radiators.

do you mean that some rads are hot and some are cold? if you turn off the hot ones, do the cold ones go hot?

Are rads hot all over, or patchy?

 

[BinM]

Thanks for your help with this, the diagram that Stem posted is exactly what I have and now I understand how the hot water cylinder is connected to the boiler.

There is also a little more to my story. The system has recently been power flushed as it hasn't had any maintenance in many years and was suspected as being full of sludge. And indeed the flush did clear out lots of black sludge.

Since the flush it's been difficult to get all of the air out of the system with a couple of rads continuously collecting air.

When radiators get hot they are evenly hot so I'm fairly happy the system and rads are clear.

Yes, when you turn some rads off others start to work, plus the house has been extended at some point with the addition of rads so I'm suspecting the pipe layout isn't ideal.

I'm guessing it's lots of balancing and bleeding for me!!

Thanks again for the help

 

[stem]

When you had the system powerflushed, it would have been filled with fresh water. There will be some air in that water, which combined with the odd pocket or two of air trapped when filling, may take a while to come out completely.

I assume that corrosion inhibitor added was added after the powerflush, otherwise the water will corode the radiators and create air and new black sludge.

 

[BinM]

Inhibitor hasn't been added yet, it's on the list of jobs for this weekend. I wanted to make sure I wasn't going to have to drain the system for any reason before I put it in.

I've read in a few places that it's a good idea to test the pH of your system to ensure the water is good and neutral (pH of 7) adding chemicals to adjust it if necessary. I've not heard of this before, any thoughts or suggestions??

 

[stem]

Do leave it too long to add the inhibitor, corrosion will start immediately and guess what? The corrosion process also produces gas.