Rads not getting boiling

[wanttolearn]

Hi guys in need of some expert advice. Drained down system today to fit 2 x 1400 double rads after fitting them put tge heating on but all rads are getting warm but not really hot as they should.
Boiler is a modena not sure which one though. On the boiler I've turned up the rads to full heat and the thermostat up full but on the boiler the temp is not going up any higher than 40.
Going back to balance the system tomorrow to see if that helps but don't think it will.
Any idea what could be the issue?

 

[Rickster123]

How many rads on the system? Did you swap rads like for like or were they added to existing rads?

 

[wanttolearn]

6 rads on the system and just replaced these as there were 2000x500 single and 1400x500 single

 

[Rickster123]

And the system water is clean?

 

[wanttolearn]

Yes it was clean when I drained down

 

[acecharly]

maybe airlocked

 

[NickDavies]

Delta T (foxtrot oscar) had a similar job once, national service contract company refused to make any further visits to the premises regarding cold radiators, the by-pass was red hot and a single towel rail in the bathroom was red hot, everything else was luke warm.

The flow and return was run completely in 15mm plastic pushfit about 20 years old by the look and colour of the fittings, there were several sections of pipe that were completely choked up with thin sections of scale deposits that had dislodged from the bore of the plastic pipe and shifted to pinch points where they just dammed up and totally blocked the bore of the pipe (the only real circulation taking place was through the towel rail and the F & R bypass.

Of course I only found this out once I had spent a few hours cogitating all the possible causes or omissions and lifted some floor boards after draining down..... the system was very slow to drain down even with every air-vent wide open so I suspected some kind of blockage by this time. I had photo's but I don't keep the everyday stuff on my phone too long. but the pipes were solidly blocked with paper thin slithers of rusty brown scale, the job turned into a partial re-pipe in 22mm with a power flush after and the instruction to always use fernox or similar inhibitor......some of these modern cheap pressed steel radiators you can find these days for a few quid are not helping I'm sure, but generally deposits stay stuck to copper pipe bore but not plastic too well, so this might be worth having a look at amigo, if it is indeed a plastic flow and return.

 

[wanttolearn]

Yeah I did notice there was a small bit of plastic push fit underneath the boiler but unsure on how much. Will be having a good look tomorrow and see what the hell is going on

 

[wanttolearn]

It's a mainline 30he. I think it's air locked up put tge heating on fires up starts heating up rads goes up to 60 and then the light for pilot goes out and temp drops on boiler.
So am I right to think it's a air lock. I tried knocking all rads off except 2 one with hoze attached and opened up filling loop to push the air lock out. But to no avail.
Any other recommendations

 

[Stigster]

Powerflush?

 

[ShaunCorbs]

Can't have push fit anywhere close to the boiler need a min of 1m copper pipe

 

[Last Plumber]

Did this system work before you changed those rads ?

If a system is in working order it's always good to test it works before you alter anything just to be sure, in the same way, always fire a boiler prior to servicing it, just to make sure it will.

Did you check that the pipe sizes are adequate for the larger rads ?

What is the pipe size leaving the boiler and where does it decrease ?

Those two rads @ 1400 x 500 doubles ( I presume its 500 like the ones you removed ), are around 7500 to 10000 btu each depending on delta T and make. there are two off, so what else is on the 15mm you mentioned ?

As a rule of thumb in my head !

( and before anyone comments, this is in my head and not official and I'm not asking for agreement or opinions on this or criticism and I'm not responsible for anyone following this and using it as advice ),

But !

I always think on a sealed system just under 30000 Btu's/hr Max on 15mm copper and on open vented around 25000 Btu's /Hr max. 15mm copper. (plastic is a wee bit smaller bore)..

If you're over that it will reduce ( because it's shared ) the heat you can dissipate from the amount of water you're shifting in an hour.

I may be off the point here, I'm thinking out loud but it's worth checking.

From how I read it the boiler fires and makes it's way up to 60 deg ? is that what it is set on ?

If it is and it gets there it could be going off and falling in temp due to anti-cycling timer in boiler if it has one. If the pipe size is under for the emitters output it will fall quite quickly after the burner goes out.

Sorry to go on !

 

[wanttolearn]

I did not check the heating at first as customer saI'd haven't used it all summer but the rads used to get very hot.
Pipe size is 22mm leaving the boiler and then drops down too 15mm. There are 5 rads on the system altogether.
I've turned the boiler up too max temperature and thermostat up full but still not solving the problem.

She did say boiler is in need of a service as it's not had one in a while and then said the hot water is not as warm as it used to be. So I'm really hoping that there is a issue with the boiler?

 

[Last Plumber]

What are the flow and return temps at the boiler ?

 

[joni os]

Turn off all rads except one nearest boiler, fully open valve and balancing valve.( If thermo valve, ensure pin moves freely). With heating call this rad should get hot irrespective of pipe sizing. Failure to reach working temperature indicates circulation or boiler problem. Look for evidence that eliminates a hypothesis rather than form an opinion and seek evidence to confirm it.

 

[wanttolearn]

Thanks for all the help guys appreciate it cheers