New radiators colder at the bottom even with powerflush

[noddy997]

I had 10 new rads fitted, powerflushed and a lot of magnetite and sludge came out from the pipes.

However they still remain cooler at the bottom than the top. There can be a 4-10c difference between the top and bottom. I have measured with a infra red / laser thermometer.

Any suggestions? Will replacing the pump help?


Cheers

 

[Madrab]

If the radiators are new and the pipework is all clean then it has to either be a circulation issue ( lazy pump) or the boiler output/setting isn't setup correctly.

That being said you will always have a temp differential top to bottom until the space is warm enough as the radiators will lose their heat and the cooler water will be to wards the bottom, that's how they work, if you see what I mean. There should always be a temp differential between flow and return, determined by the deltaT

 

[noddy997]

If the radiators are new and the pipework is all clean then it has to either be a circulation issue ( lazy pump) or the boiler output/setting isn't setup correctly.

That being said you will always have a temp differential top to bottom until the space is warm enough as the radiators will lose their heat and the cooler water will be to wards the bottom, that's how they work, if you see what I mean. There should always be a temp differential between flow and return, determined by the deltaT

I've changed the pump too this evening, same issue.


Elaborate on deltaT please? The temp differential was 36 and I have managed to get it down to 20-22 when it has been running for 2 hours and the rads got up to 50c at the top! Done this by down rating boiler from 38kw to 24kw and setting the boiler flow to 68 and then dropping it to 64.

Would you recommend upping the size of the gas pipe? It's currently got a 15mm on a long run of 16m with plenty of elbows and with a T for the cooker and the fire place. Would it help heat the rads more say if its a 28mm run?

Cheers

 

[cross thread]

Without testig gas pressure and gas rate we can’t tell you ,but it sounds undersized.

 

[Madrab]

+1 - it needs gas rated to see how it is performing but as suggested that size of pipe on a 36kw boiler would usually never cut it on it's own, never mind with a cooker and a fire too.

Delta T Explained

 

[75pete]

Is it practical/ possible to take one off and back flush it, will give you an idea if it’s and others are still part blocked.
*just seen, all new rads

 

[Johntheo5]

Your temperature gradient should be like mine below.

 

[Higgy28]

If your radiator was the same temperature at the inlet and outlet it wouldn't have given out any heat to the room!

 

[noddy997]

Your temperature gradient should be like mine below.

Sorry don't understand the figures

 

[Johntheo5]

The numbers in the diagrams are the rad temperatures taken with a IR gun, the top one where the pipes are connected in to the bottom of the rad (normal installation) should give a fair indication of the temperatures you can expect if set the boiler flow temperature to 65C.

 

[gas112]

38kw boiler/cooker/fire on 16m of 15mm yep gas is massively under sized