Central heating 'Reversed Flow'

[chewymix]

Hi

I may not have the correct term but i think the water is flowing around my central heating system backwards and resulting in poor performance in terms of even heat output from the radiators. Let me explain and i'd like some input.

I had a new boiler fitted when we did a kitchen extension a couple of years ago and hot water has never been a problem but i have noticed that the radiators heat up unevenly, ie some are pretty hot and others a only warm. Its not really been a massive problem more something that annoyed me so i started to look at balancing the system to try to even things up. One of the tasks in balancing seems to be trying to ensure a 12 degree temp drop between inlet and return valves. In investigating this its clear that every single return valve is HOTTER than every single inlet valve which strikes me as the flow going actually being pumped around the wrong way. I guess this was just a massive installation mistake but has anyone heard of that before or equally what can be done about it? I do know that i didnt think much of the plumber when he installed everything but its evidently clear if my suspicions are correct that he may have been a plumber but he certainly isnt a central heating engineer!

The boiler is a Worcester Bosch and the CH is a vented system with a couple of motorised valves, one that operates the radiators and the other which send water to the hot water tank.

Is my guess at water going the wrong way likely to be true?

 

[JohnD]

how are you identifying the F and the R valves?

 

[chewymix]

Inlet valve on the right which might be a TRV but generally not on the older rads. Return is on the left and is a lockshield type valve and its this side of the rad, on each rad, thats hotter than the other.

make sense?

 

[JohnD]

Nope.

 

[gigz]

If they are bi-directional trv's it doesn't make much difference which side the flow comes from. Water takes the easiest path so as you can imagine, 99% (if not more) of systems will heat up unevenly. First thing to do is forget about the 12 degree F&R difference, thats lab conditions written by a know FA penpusher. The rads that get hot first, close the trv/wheelhead, then check the luke warm ones are getting hotter (this will rule out sludge/dirt and prove its a balancing issue). If they do open trv/wheelheads but close the lockshields down a touch. Its a case of trial and error to get it spot on. You can use a thermostat to help but usually using your hand will be good enough.

 

[45yearsagasman]

Was it a simple boiler change, or were there other parts of the system altered in any way?

 

[chewymix]

We only have 2 trv's in the whole system but the fact is the lock shield valves are way hotter than the inlet valves on all the rads.

The boiler was swapped but lots of other changes were made. The hot water tank was also swapped out along with the addition of the motorised valves as this boiler replaces an old baxi so plenty of opportunity to get things wrong I guess.

 

[45yearsagasman]

Not necessarily wrong, but how they may have connected back into the existing ch pipework may have caused water to flow opposite to what it originally did. I've seen that many times when converting from a gravity HW system to fully pumped.

 

[Agile]

If I am understanding you correctly you seem to imagine that the inlet should be on the right?

It can be either side.

The TRV can be put either end although they are usually a little quieter on the flow but also control the temperature slightly better on the return.

Nowadays we are usually working on existing systems and have to accept how they are already connected. I put the TRVs on the cooler end of the room or the most accessible end if that's relevant.

Tony

 

[chewymix]

It's not that I expect them to be I the right or left its just that the lock shield valves are on the left on all my rads and this is the side that has a higher pipe temp hence me assuming the flow had been reversed during the install.

Is there anything else that could cause this and if not how can it be fixed?

 

[JohnD]

You are assuming that the lockshield "should" be the return.

Discard this assumption.

The problem you have is that your radiators are not balanced. So balance them.

 

[D_Hailsham]

There is probably no need to "fix it" as, from a heating point of view, it doesn't matter which way the water travels round the system. What is important is that the pump sends the water through the boiler in the correct direction. If the pump is built in to the boiler it will be correct; but if an external pump it will normally be on the flow side, pumping away from the boiler (arrow on side of pump). It can be on the return side (rare), in which case the arrow should point to the boiler.

As for the lockshield valves on the "wrong" end", that is normally easy to rectify by swapping over the wheel head and LS cover. Obviously you can't do this with a TRV on one end, but it really doesn't matter if you have a bi-directional TRV (two arrows on the body).

Rad valves control the flow through a radiator; they have the same effect irrespective of which end they are on.

 

[chewymix]

Hi - i dont believe the boiler has a pump in it as if it does then we have two!

These are some pics of the pump and the valves - the valve on the right is for the rads and the one on the left is for the HW - I have no clue how i would work out which side of the boiler from a flow point of view this is, any clues as to how i could check?

cheers

 

[45yearsagasman]

I would contact the people who installed it and simply ask the question. That's not the best example of the heating engineers craft that I've ever seen.

 

[D_Hailsham]

I have no clue how i would work out which side of the boiler from a flow point of view this is, any clues as to how i could check?

Which model WB boiler do you have?