Last radiator not reaching full heat

[gemius]

Hi
I've a new Worcester Bosh boiler serving 9 rads in a medium semi. The last rad on the system (a brand new rad) refuses to heat up fully. although the pipe work leading to it, and all the other rads get too hot to touch. Thinking about it after the plumbers had gone, I wondered, if there was a blockage in the flow immediately before the last rad, would the water still circulate back to the boiler from the penultimate radiator with this result?
The plumbers who fitted the rad seemed to think there just wasn't enough flow pressure to force it through. Shutting down the other rads does improve it, but it still doesn't get as hot as the others despite the flow being red hot just before the inlet valve.
Your comments would be appreciated.

 

[Deleted member 267285]

Lockshield definitely open? Sounds like a balancing issue.

 

[gemius]

I fear it is but last winter I had to turn all the other rads down too far before I got any heat in the last one, which is my dining room. Hence the new boiler and new rad. The previous boiler was quite old.
I still can't understand why the flow can be red hot up to the rad and then the return only luke warm. I understand the heat has to dissipate somewhere but I'm surprised it can't make it through all the radiators. The plumber who fitted the boiler said it was powerful enough to heat next door as well and I believe him.

 

[ericmark]

The whole system has changed from the old fixed output boiler. The idea is to control the boiler output by monitoring return water temperature.

So if water from any radiator returns hot then boiled output is reduced, so balancing is critical.

Idea is once all rooms are at required temperature the TRV's will all close and the by-pass valve will lift sending hot water back to boiler that will then turn off. But before this the return water gradually gets warmer and the boiler reduces output.

The lock shield is set so with all TRV heads wide open there is around 15deg C temperature drop between supply and return.

 

[Deleted member 267285]

Is it a standard radiator and not a towel rail, or column radiator?

 

[oldbutnotdead]

Take it the pipework wasn't renewed. Any way of checking it, could be all sorts of nonsense under the floor restricting the flow.

 

[gemius]

View attachment 239957 View attachment 239957
Thanks for your input. It's a standard rad CBW but the WC rad is a small column rad and though I didn't mention it before (apologies) it suffers the same problem.

Pipework wasn't renewed. However it's easy to expose and the last two rads (it backs on to the WC) are taken off close together.

I don't see how it can be done any different and I'm coming round to thinking it is a balancing problem and I've just got to make the best of it.
Just one more thing. If I want to balance the rads as to the book, how do I take the temperature? Is there a special thermometer which attaches to the pipe ?

 

[oldbutnotdead]

That tube run under the floor (that the rads tee off) looks like 15mm to me. If the rest of the distribution pipework from the boiler is 22mm or there's a manifold somewhere so the 15mm is only feeding 2 or 3 rads then fine, if it's all 15mm from boiler round all the rads without a manifold then you could be into significant headloss, possibly greater than the pressure differential the bypass is set to (assuming there is a bypass).
Balancing will be a good start, plenty of guides on how to. Non-contact IR thermometer is fine, or get a couple of £3 led thermometers and use clothes pegs to clip the probes to the rads.

 

[gemius]

It's all 15mm I'm afraid, so that might be the crux of the matter. It must have been fitted late 1970's and it worked fine then, but I'm now on my third boiler. It's position in the house was changed when the second one was fitted and rads have been added so I can't complain. Replacing pipes is not an option. Too much disruption.
Thanks for every ones input

 

[oldbutnotdead]

Try balancing, it might improve matters. And you wouldn't have to replace all the pipework to make a difference, just a few key sections. Not a job for remote assistance, a heating engineer (not a boiler slinger) would need to have a look

 

[Deleted member 267285]

If the wc rad is column, and the feeds are after that, then it could be that it’s not fitted correctly, eg right way up, I’m led to believe there are baffles inside?

 

[gasbusters]

System needs rebalancing