Cold rads intermittent boiler - PLEASE HELP

[coldandtired]

I have a Potterton Netaheat 50 which heats 5 rads downstairs and 4 upstairs (incuding a bypass rad in the bathroom). It is an open vented, fully pumped system fitted with a combined feed and vent.

During the summer, many of the rads were removed for redecorating and the valves fully opened on each end. When the heating was needed a month or so back, I noticed that only the downstairs rads were working.

I had the boiler serviced and the engineer said that the upstairs was not working due to a blockage in the system which needed power-flushing. I did not book him in but consulted Google.

I found several forums where people had similar probs to mine and one excellent answer which advised them not to proceed with a power-flush until they had ensured the system was “balanced” – especially if rads had been removed for decorating!

I tested the system by shutting off the downstairs rads and surprise, surprise, the upstairs ones all worked! - proving that the engineer was a liar out to fleece me for a few hundred quid (he had also said that if the power-flush did not solve the problem, then he would need to replace the pump as well).

Unfortunately, I cannot balance the system as recommended (I have no thermostats to start with) and the boiler only seems to work for 3 minutes before cutting off for about 10.


I stated by shutting down all the rads and only having the downstairs ones open a quarter of a turn, but the boiler only runs for a few minutes before shutting down for about 10 – and this was taking all day. I assumed that this was because no water was getting through to the rads. I then tried doing things in reverse by starting with all the rads fully open and then seeing how much I can close them without losing too much heat. I decided I should try shutting down the bypass rad (as that seems to be the only one getting hot), but that shuts down the system and I have to press the reset button under the boiler.

Even with all of the rad valves fully open the boiler only runs for about 3 mins before shutting down for 10 and I seem to be getting nowhere. It is a freezing cold day (temp should get up to about 4 degrees outside). My room stat reads 12 degrees and is calling for heat.

CAN ANYBODY HELP ME PLEASE?

 

[2face]

sounds like an air lock in the primaries or seized pump.
its very hard to tell without seeing it .

but i would go for air..

i would say it is coming to temp and the boiler stat is shutting the boiler down. after 10 min it has cooled enough for the boiler to re light.

then off it goes again 3 min warm up and shut down.

if it has been piped up a bit rough this can happen when you drain a system down.

1 way round this i have found usually with the open vent systems or the old back boiler systems was to back fill the system.

might work for you.

drain down the system. remove a rad. connect a hose to the copper leg and connect the other end to an out side tap.

fill the system from downstairs. get someone to sit in the roof so the expansion does not over flow.

remember to open the zone valves manually or turn the programmer on calling for heat but shut the boiler to the off position.

now try the heating ..

let us know how you go on .

before anyone starts bleating about if this will work or not .. lets see what happens .

 

[coldandtired]

Thanks for the advice.

I will try, does it matter which pipe I attach the hose to?

Also, would this "flush the system at the same time?

I do not have anyone to hel, so would it be safe to set it running and then keep checking in the loft?

Cheers

coldandtired

 

[coldandtired]

Hi 2face,

I should also add that the pump seems fine as it heats the water okay, and when the downstairs rads were shut all the upstairs ones worked and vice versa.

thanks again

coldandtired

 

[gas4you]

Unfortunately, I cannot balance the system as recommended (I have no thermostats to start with) and the boiler only seems to work for 3 minutes before cutting off for about 10.

You do not balance the radiators with the trv's (thermostats), you do this with the other valve, the lockshield.

 

[MANDATE]

I'm just picking up on a couple of clues here but I could be off track.
I note it's a fully pumped sysytem and I'm thinking you will have a 3 port valve. There seems to be lots of problems with 3 ports where you can't get CH only. But when both HW and CH are selected you do get CH for a limited time.
What happens is that the HW soon gets satisfied and the valve is supposed to move to CH only and either it does not or if it does it does not light the boiler.
So your HW cools a little or is used and boiler lights, the HW used is replaced and at the same time ( couple of mins) you get some heat to the radiators.

 

[coldandtired]

Thanks to all of you that are trying to help, it is much appreciated.

In response to the suggestion from gas4you, I have been using the lockshield valves to blance the system.

In respose to MANDATE, unfortunately it is not a 3-way valve, but 2 x 2-way valves, one for the hot water and one for the central heating. I have turned off the hot water whilst I resolve the problem....if I can resolve the problem!

Thanks

coldandtired

 

[2face]

open the zone valves manually to check them. using the steel lever on the side.. depending on the model.

and yes you can do this alone .. if the tank over flows it should escape down the over flow pipe if fitted correctly.

 

[coldandtired]

Thanks 2face....here goes...I guess it does not matter which of the pipes I attach the hose to, or better still, sould I send a blast of water through each one?

I will secure the hose with a jubilee clip so that it does not come loose under pressure.

Yes the motorised valves have the little levers that lock open, but do I need to invove the hot water side as well?

Cheers

coldandtired

 

[2face]

does not matter which you use. also open the hot water to might as well fill it all correctly.

ideally place a piece of copper in the both valves say 4 inch long.. then using a push fit straight coupling into the hose.

you could then swop them as you see fit also you can test the system when full.

just turn off both the valves and fire it up.

you can then drain from this point to .. if you wanted to retry t.

good luck

 

[coldandtired]

Thanks 2Face,

I'll let you know how I get on. I am just off to the plumbers merchants to get the copper pipe or see if they have anything purpose made, I'll get some inhibitor whilst there and some of that gunge reducing stuff which I can put in the system whilst I am draining it and can leave there for a few weeks.

Cheers

coldandtired (and a little smelly if the truth be told) - but looking forward to a hot shower and a warm house!!

 

[coldandtired]

Hi 2face,

I have now back filled the system and run plenty of water right through. I had the rads all closed, the feed from the tank closed, the vent stopped off, the boiler off but the motorised valve open for the heating side only (I chickened out of doing the hot water side as well on the principle that "if it ain't broke, don't fix it").

Unfortunately everything is still the same.

The pump works, the valves open as they should, the heating fires up, but then does not seem to circulate the hot water, so it closes itself down.

HEEEELP!!

coldandtired ... now even colder and even more tired!!!