Faulty pump or return blockage

Hi,

I am in the process of having a new conservatory fitted. Part of this process involves moving a small radiator where the doors to the conservatory will be onto a different wall.

Now this little rad has been giving me problems for a while. It doesn't heat up fully (or at all sometimes).

During the moving process I changed the rad to a bigger one too. Now the problem still persists with the new radiator. When the heating is turned on the flow pipe is red hot, but the return is cold. I have checked that the values are open, also the valves are new with the rad, so should rule out faulty valves. After 15 mins or so the flow then goes cold and the rad has a very small amount if heat. Return pipe remains cold.

This radiator is the one furthest away from the pump, the living room one is also not as hot as the others but acceptable (prob 2nd furthest away). All other rads are hot and cannot touch for any lengthy period of time.

The pump is somewhat noisy to. Instead of a smooth pumping sound, it has somewhat of a beating noise to it, is this normal?

I have bled all the radiators and the pump, and when emptying the system the water is quite clear, no sludge as far as I can see (although the house is only 8 years old so wouldn't expect to see much)

From reading various posts, it sounds like I could have

1. Blockage in return pipe
2. Faulty Pump
3. ?

It's a sealed system running off a standard boiler (not a combi) and tank.

Sorry for the essay, but thought I would throw in as much info as possible.

Thanks.

Sounds as if it may need balancing! See the FAQ !

The pump should be fairly quiet. Are you sure you have bled it correctly and the valves are fully open?

The bucket test ( see FAQ ) might identify flow problems.

It it microbore?

Tony Glazier

I have tried balancing at no avail and the valves are certainly open. How good a balancing job without pipe thermometers I don't know though.

But I am sure in the past I closed off all other rads apart from the problematic one and it still didn't work correctly.

It's 10mm microbore feeding the last parts of the run to the rads (behind all the drywall runs), but the underfloor runs seem to be 15mm with 10mm reducers. Although haven't been able to confirm this will all rads, only the one I have moved since I took the floor up ready to spur from the bedroom up stairs since I have been told that spurring of 10mm microbore is not a good and both rads would just remain luke warm.

Had another good read through the FAQ, and invaluable resource I must say.

One thing I have missed which I believe could be (and hopefully is) the issue. I think I have the bypass valve fully opened, so like the FAQ says because of the less limiting path for the water to go, it all travels through the bypass instead of going to the rads furthest away.

Would this type of behaviour fall into the fully opened bypass value scenario?

Thanks.

On a microbore system you need a higher pump pressure.

Opening a valve type bypass any more than a fraction will prevent thre system working. Probably you can close it completely if at least one rad has no TRV and its a three port valve.

It should be an auto bypass valve.

If there are still problems with that rad then do the bucket test.

Tony

I think it's a 2 port valve from the top of my head. I'll check again tonight when I get in. Am I right is saying a 2 port valve is basically an in/out yet a 3 port value is a T shaped?

All upstairs rads have TRV's, all downstairs rads don't, apart from the one I have just replaced and moved and the new one I have scheduled to be put in the conservatory.

So if I shut the bypass value completely am I right is saying that as long as 1 of the rads downstairs always remains open it shouldn't cause me any problems. Or should I just open it just a shade to be on the safe side.

Thanks.

In spite of your essay then we dont know your boiler make.

If it has pump over run then you do need the bypass open a TINY bit.

See the FAQ on how to adjust them.

Tony

Sorry, should have included that. It's an Ideal Icos HE15. I'll open it a small amount, 1 full turn suffice?

edit:

Although does make me wonder why they don't put an automatic pressure value instead of the manual valve so that it remains shut when it should be shut.

I have no idea what type of bypass you have!

Whatever you say its probably too much!

Tony

OK. Thanks for your help Tony. Appreciated.

I do have another question if you don't mind.

Would 10mm microbore tails from the 15mm underfloor runs be OK to heat a 8000 btu rad in the conservatory, the tail length from the 15mm will be about 4.5m.