Random radiators working

[jackso]

We installed a 30kw boiler to a detached house with 18 rad system and pressurised cylinder about 7 months ago.
Every couple of months the customer rings to say some of the rads work and then don't the next day and that it is random all through the house on different days. We have been back many times and balanced and played with the system and always left with all rads boiling hot.
The house was built ten years ago and after speaking to the customer we have gathered that neither the builders or plumbers were that brilliant, so how the pipework is run and what sizes etc under floor who knows!
We took out a floor standing 35kw combined boiler and storage tank made by a Scottish company I believe but was a pain for the customer to get fixed as nobody knew anything about them. He says the rads worked fine with the old boiler.
We are starting to think that there is something a miss with either pipework runs under the floors or air being sucked in etc???
Any experienced engineers out there that could offer some help? it would be greatly appreciated.

 

[Ermintrude]

Sounds like it will be 10mm off of a manifold, probably some debris bouncing all over, trvs might also benefit from being changed!

 

[missplumb]

could it be that the pump isnt capable of powering all the radiators all the time, its easy to balance rads to get them all hot when actually, some are cooling as others are heating up. i guess all the radiators are reasonably small as a 30kw for HW and HTG sounds a bit small.

 

[Ermintrude]

30kw for heating and DHW is massive for some houses! Get back to your 2mW

 

[jackso]

As Ermintrude says a 30 kw system boiler is alot of power. The customer has turned off 3 large radiators and still has the same problem with random radiators working even some very close to the boiler. If the boiler wasn't big enough it would work fine once the 3 large rads were turned off, essentially taking 5kw off the system.

 

[Ermintrude]

I was in a house other day . "Nice custard, bang tidy in fact" 3 bed semi 1 bath 17lpm Ok dumb bum. Boiler and rads full of cavity wall poly balls. Balls were obscuring manifold randomly. 10mm copper.

 

[Whyme]

I agree with ermintrude defiantly sounds like something meandering around the system, had one on a system with 15mm feeds. the only way i could convince customer it needed a good flush was by getting him to hold the flow and return on a sluggish rad and i hit the lockshield with a nylon hammer. he soon pulled his hand off when it got hot.

 

[acecharly]

If its random radiators that are affected, and that when you go around and have a tinker they all come on its not the boiler. Id put some cleaner in for a while and give it a good flush through whatever it is sounds like its wandering round the system.

 

[jackso]

Hi Missplumb
Just like you to know you were right regarding the pump. We have fitted another 15-50 on the pipework aswell as the integral one on the boiler and it works a dream ! everyday is a school day !! many thanks

 

[lame plumber]

30kw boiler and 2 pumps for 18 rads system omg!!!!

 

[Whyme]

fit a 15-60 as well have a three pump and the crap will have no chance of settling..

 

[Ermintrude]

Or a 25-80 on full rattle