Has the motorised valve gone?

[dirty harry]

Help needed please!

My uncle's house has 11 rads fed via microbore, a brand new Grundfos 15-16-130 pump and a 15-20 year old Potterton Netaheat boiler (serviced every year and heats water ok). Few weeks ago he asked me to look at a non-working rad in the bathroom. I noticed the lockshield valve was fully open so I closed it off, opened it a 1/4 turn and hey presto one very hot rad. However, one of the three very large rads in the lounge (all 6ft high!) didn't work, even though hot water was getting to the TRV it just wasn't filling the rad. I bled it and released some dirty water but it wasn't dirty enough to suspect a blockage. Due to time constraints it was left as is.

Yesterday he called to tell me the bathroom rad was no longer working, the 6ft one in the lounge still didn't work and now a rad in the hallway had just stopped working overnight. I've bled the faulty rads, checked the balancing on all rads, checked the pump for air and released some of the water via the drain port near the hallway rad to see if it was blocked with sludge, again no problems. So now I am baffled.

However, one thing I did notice was, bearing in mind the heating was on full, when bleeding the rads the pressure was very low, not really a dribble, but certainly wasn't coming out with the force I expected. Also, despite the thermostat being set to high, the boiler kept switching off. I have also been told the CH is noticeably cooler when the Hot Water comes on.

Anyone have any tips on what the likely problem is? Is it the motorised valve? Could the Grundfos be faulty (all three speeds seem to work ok)? It just seems there is not enough pressure in the system to force hot water to all the rads. I had also thought maybe the microbore is blocked somewhere under the flooring but clean water seems to be getting to the cold rads so I don't think that's the problem?

Any thoughts anyone? Cheers.

 

[darren17]

have you pressurised the system
microbore is prone to blockage
is this one sealed or open vented

 

[dirty harry]

It's open vented and the header tank is filling the system up ok. Apparantly another plumber changed a towel rad last year and when he took the old one off he was covered in a flood of black sludge! I suspect there may be blockages somewhere in the system. Is the only solution to have to pressure blasted?

 

[darren17]

instead of paying for pressurised flush you can flush with mains that should clear enough so you can add say a fernox system restorer.
do you know how to do a mains flush???

 

[darren17]

did the plumber that fitted the towel rail after seeing the sediment not advise to get the system cleaned???

 

[dirty harry]

did the plumber that fitted the towel rail after seeing the sediment not advise to get the system cleaned???

errr..... no. Some plumber he was! He was the same plumber who left the lockshield valves fully open on 4 of the rads.

I've never done a mains flush on a vented system so would be grateful for any tips!

 

[darren17]

this is what you need to do !!
drain down the system completely
make sure to turn off the feed from the f+e tank
then close the wv & lsv on all rads except 1
you have to join the expansion and feed pipes at the small tank and close the iso valves at the pump
once you have done all this take off the rad that you left open and connect a hose from the mains and then connect a drain hose to a suitable drain
you will have to connect bit's of pipe to the hose so you can connect to the flow & return rad valves
now open the valves on another rad and you can turn the hose on
let it drain from hose till water runs clean then turn off water and do the same to other rads 1 at a time

when this is done you can change the pipes over to the return for water and flow for drain
once all the water comes out fairly clean you can replace the rad and open all rad valves
open the iso valves at the pump
disconnect the pipes at the f+e tank and connect the feed
just refill the system and add a fernox heavy duty restorer leave all valves open fully for about 1 week
after the week simply drain the system and flush a few times then refill and balance rads
it would be a good idea to add two valves while the system is drained so as to be able to do this when needed
microbore is prone to blockages
you can add an inhibitor fernox f1 to your system to prolong the life of your system
anymore questions feel free to ask!!!!

 

[dirty harry]

As a famous meerkat once said .....ssshhhimple

Many thanks for the very detailed instructions! Very much appreciated.