Replaced two Radiators, been told we now need to replace pipes feeding radiators…

[IanM18]

Another question time (sorry) I was reading that the ideal temp difference between the in and out should be 12 degrees?

So if going in, it’s say 58, and coming out it’s 32, is that within normal range, or would I open or close the lockshield a bit to adjust?

 

[terryplumb]

Close down the lockshield ,a little at a time ,to achieve the temperature differential

 

[IanM18]

Thank you!

 

[Kissarmy]

Closing the lockshield down sounds wrong to me. If the input is 58 and the output is 32 then surely there is too little water flow through the radiator as it is radiating away 26 degrees by the time it leaves. I would think opening the lockshield valve would allow the water to get from the input to the output quicker and thus radiate less of it's heat away by the time it leaves. If it's 58 on the input you should be aiming for 46 on the output.

 

[IanM18]

Morning everyone, firstly, thank you all for the thoughts/suggestions - really appreciate it.

Just a quick update, have been playing with the balancing, have managed to get 99% of my radiators hotter, and one of the two new replacements that’s being problematic, is also warmer.

The final radiator is being stubborn.

With everything else off, it gets red hot, with everything on, red hot at the top, lukewarm at the bottom.

Plumber is suggesting replace pipework at a cost of 1k, and that may fix it, and if it doesn’t he can do other pipes for another 1k, and that may fix it, but if it doesn’t, it could be the boiler pump or something else entirely.

Not keen on paying 1k for a “this might fix it, but might not”.

They worked before, now they don’t.

Have been nosing around, and the only difference they made when replacing, was the had to extend the pipes a little, as the new rads sit closer to the wall, so they cut the pipework, and extended it using plastic push fit/compression angle connectors, rather than the old copper pipe that just went straight up.

Could that be contributing to the problem?

 

[Why Not Indeed]

they cut the pipework, and extended it using plastic push fit/compression angle connectors, rather than the old copper pipe that just went straight up.

For the same OD, plastic usually has a smaller ID:

Plastic vs. copper in central heating

Is the flow resistance of plastic pipes the same as copper or not? Would a 10mm plastic pipe have the same internal dimensions as a 10mm copper pipe? I can't find any data sheets for plastic on the web.

www.diynot.com

So yes, it could be the problem, but not 100% clear from your description if any plastic pipe is in use, or just some plastic fittings. Maybe a picture would help.

 

[DP]

Plumber is suggesting replace pipework at a cost of 1k, and that may fix it, and if it doesn’t he can do other pipes for another 1k, and that may fix it, but if it doesn’t, it could be the boiler pump or something else entirely.

2k to possibly fix an issue and that is not guaranteed either. Do you live in a castle?

Do you have plastic pipes feeding problematic radiator?

Looking at some previous posts, some unhelpful posts.
If the boiler has cast iron heat exchanger, then the temperature drop between flow and return at the boiler should be 11 degrees C
SE tended to be similar temperature but difference could be greater but not more than 20 degree C. Look at the nett and gross ratings for this boiler. Gross is higher than nett
Condensing boilers. Gross and nett ratings nearly the same hence boiler is 95% efficient at startup from cold.
Condensing boilers need to have 20 degree differential between flow and return for sake of efficiency ( extraction of heat from flue gases)

Having established the differential at the boiler, balance the system for same differential at each radiator.
If differential cannot be achieved then either pump speed too low to overcome system resistance or pipe undersized or blocked.

Plastic plumbing, the preferred option for most plumbers can block up unless necessary steps are taken. The system water which has metal oxides and metal particles ( magnetite), as it flows through the pipes, will deposit a layer onto the inner wall. In plastic plumbing this layering will be film like and when it dislodges, will flow downstream and can cause restriction and blockages. At times this blockage can be like the leaves on a sink outlet stoping sink from draining and other times a crusty sponge like blockage that can be cleared up if rodded but here pipe replacement is most times the answer. Pressure will not dislodge the blockage even on a short run.

Hope above useful as these are scenarios not imagined but encountered while faultfinding. Have three radiators on a system am working on- two of the rads are 15mm plastic, flow into first two is nice and hot and return is poor hence rads do not heat up and third is 10mm copper micro-bore, further away, plumbed from previous two is poor too because of poor delivery due to plastic plumbing it is fed off. These radiators are in the extension that was added to the house. Rest of the house all copper, no issues.

 

[IanM18]

Sorry for the late reply, have been forced to endure Christmas prep.

Thank you for that, all makes total sense.

We have a condensing boiler, think it’s the valiant ecotec 835. It’s about 15 years old.

The only plastic bits are the right angle joints where they had to adjust how near the pipes were to the wall, told us radiator brackets had got slimmer, so rads sat closer to wall.

is there anyway to test the pump speed?

They did say that under the floor we had 5 radiators on one spur (I think that’s what they called it, like a run of thinner pipes off the main flow?)

They want to split them into two, said having 5 on one set of smaller pipes will cause resistance, and that “might help” Funny thing, we had the 5 before and they were working perfectly.

Really don’t know what to do next, feels impossible, but checking pump speed might be a first thing to do?

 

[IanM18]

And just been reading boiler manual, it has different pump speed settings?

Default is 0.

Manual suggests 5/Comfort/full setting for a multi zone system.

Guess it’s worth a check.

Anyone know how to check what it’s set to?

 

[spile]

The final radiator is being stubborn.

With everything else off, it gets red hot, with everything on, red hot at the top, lukewarm at the bottom.

So this is what I would do,,,
Close the lock shield valve on every rad apart from the problem one. Starting with the downstairs rads open the LS valves one at a time just enough for them to warm up. Then move upstairs and repeat the procedure. Key thing is to only open the lock shield just enough for them to get warm.

 

[Andy165]

What flow temperature have you got the boiler set at ?

 

[IanM18]

So this is what I would do,,,
Close the lock shield valve on every rad apart from the problem one. Starting with the downstairs rads open the LS valves one at a time just enough for them to warm up. Then move upstairs and repeat the procedure. Key thing is to only open the lock shield just enough for them to get warm.

Will try that!

 

[IanM18]

What flow temperature have you got the boiler set at ?

Boiler CH temp set to 70 on the dial thingy on the front, if that’s the same thing?

 

[DP]

The only plastic bits are the right angle joints where they had to adjust how near the pipes were to the wall, told us radiator brackets had got slimmer, so rads sat closer to wall.

More a case of not able to bend copper pipe. A copper pipe bent using a bender will be 15mm diameter, lot less than plastic fitting used.

They want to split them into two, said having 5 on one set of smaller pipes will cause resistance, and that “might help” Funny thing, we had the 5 before and they were working perfectly.

If system worked before, post rad change, will work afterwards to.

Best to carry out system balance using two thermometers. Other option is to heat all the radiators and feel the inlet pipes which should be ouch hot, then the outlet pipe that should be hot but not ouch. Any radiator where outlet pipe is ouch hot, close the lockshield a little and where the outlet is cooler, open the lockshield a little. Time consuming but end result is worth the effort

With two thermometers differential between two pipes should be 20 degrees

BTW, pipes diameter and length with fittings and bends on it, all contribute to its resistance to flow of liquid or gas within it. Someone making a bold claim should be able to demonstrate that reasoning based on facts rather than pontificate.
For example, conversion from heat only boiler to a combi, often the gas line for previous is 15mm and for combi it is 15mm at the boiler connection only. By running the new boiler flat out, one can carry out checks to show if the gas line can supply sufficient gas to the boiler and existing appliances. Printout can be supplied showing the findings