Radiator Problem

[dk1uk]

Hi all - Last week I took a radiator off to decorate behind it. I noticed whilst the radiator was off, that three radiators (in a room above our garage - extension) stopped working.

I didn't worry as I thought that when I replaced the radiator the three cold ones would start working again - unfortunately they have not. They are stone cold - the feed pipes are also code.

I have tried bleeding them to no avail.

Can anyone think why they're no longer working?

Many thanks.

 

[petertheplumber12]

try turning off any other rads and then with heating on and hot water off see if it will shift what is probably an air lock. try that first, but on open vented systems hot water must be off and any bypass loop closed.

 

[dk1uk]

Thank for the reply. How long should I try leaving the other rads off and hot water off for? Also - sorry, but what is the bypass loo - how would I know if I have one?

 

[petertheplumber12]

Have you got a hot water cylinder and plumbing for pump and a motorised valve usually in the airing cupboard? (open vented) or even unvented cylinder same setup.

 

[dk1uk]

Yes I have those things - hot water cylinder, pump and motorised valve.

 

[petertheplumber12]

ok when the flow from boiler goes to the motorised valve before it goes thro' the pump then to the motorised valve with a tee off for venting air and cold feed from F&E tank before the valve, often there is another tee off that goes straight to the return that goes back to the boiler to be reheated, and if it is there then on that loop back to return there is a manual valve that either can be adjusted or is automatic but still adjustable.
I hope that is clear enough to understand?

 

[dk1uk]

You sir, are a genius. Having shut down all but of the rads and hot water, except the cold ones, the cold ones are no longer cold! I'll let them warm up properly, then turn everything else back on and hopefully all will be good.

Thank you, really appreciate it!

 

[petertheplumber12]

you are very welcome.

 

[dk1uk]

It seems that I celebrated prematurely! Having turned everything back it, the three problem rads have gone cold again.

Having taken off rads of decorating (and therefore shutting off the lockshield valves before removing them) might I have caused a balancing issue? I've had balancing issues before but even where the flow isn't balanced normally some rads are at least luke warm rather than completely cold?

 

[petertheplumber12]

Yes it is always best to make a note of how far open the lockshield valve is before closing it. they need re balancing now. find out which rad gets hot first, turn lockshield valve off then open about 1/8-1/4 of a turn only, repeat on next rad that gets hot and so on the nearer you get to the last rad the more they are open, but lst rad is fully open, last rad being furthest away from pump. 1st rad being nearest the pump, if it is really tricky then increase pump speed from 2 to 3

 

[dk1uk]

Hi - so I have been trying various things and whilst I can get the three cold rads to heat up (e.g. by turning off all of the others in the house), I can't get them to stay consistently warm.

I have traced the pipework and can see that the feed for those rads runs off a T-joint (if that's the right term) on the main feed from the boiler. However when I checked tonight, about 2 feet along that feed that pipe starts to go cold.

When I recently got a quote for a new bolier, they told me that it was under-powered for the house (I think because the previous owners built a large extension without upgrading the bolier to cope with the 3 extra rads).

In the short-term, is it worth me turning up the pump to see if helps move the the water along the spurred feed pipe any further?

Many thanks

 

[petertheplumber12]

You can try increasing pump speed but try and get the pump on the slowest speed to get the system working properly. Assuming you had an open vented system, and you have been trying with the hot water demand deactivated, first try to visualize this:- In your garden you put a tank which can be kept full of water. O copper pipe runs from it thro a pump along one side of garden along the top and down the other side back to the tank, as long as about `80-100ft. A hole is drilled in the top of the pipe every 2 ft along its length with a smaller pipe attached to the hole sticking up in the air and a tap on each smaller pipe. All the taps are fully open, you switch the pump on and water goes along the pipe back to the tank squirting out of the smaller pipes, But the pipes nearer the pump will have a lot of water squirting out and the further away from the pump less water. By closing the taps on the pipes nearest the pump and not cooling them quite so much as you get further away you can get the water coming out of the pipes at the same amount. You just have to be careful and patient.

 

[dk1uk]

Thanks for the reply.

It turns out that when then hot water is off, the 3 problem rads heat up nicely. However, if I run the hot water and central heating at the same time, then they don't. I am guessing that the system can't handle heating all of the rads plus the hot water at the same time?

I'm getting a new bolier next year (mine is an old Potterton Flamingo that's had it's day), so in the meantime, I'll just have to time the hot water and heating not to run concurrently!

Thanks again.

 

[petertheplumber12]

Thanks for the reply.

It turns out that when then hot water is off, the 3 problem rads heat up nicely. However, if I run the hot water and central heating at the same time, then they don't. I am guessing that the system can't handle heating all of the rads plus the hot water at the same time?

I'm getting a new bolier next year (mine is an old Potterton Flamingo that's had it's day), so in the meantime, I'll just have to time the hot water and heating not to run concurrently!

Thanks again.

The hot water prob is a little bit more than whether or not it can handle it, You remember me talking about a tank in the garden and a pipe that had holes to be balanced in it? Well the prob with hot water is that the flow and return pipes to the cylinder are part of the heating circuit when hot water is heated at the same time as heating, BUT the hot water pipes are 22mm whereas the rad pipes are 15mm, so the hot water cylinder is not balanced as part of the heating circuit, Some plumbers put a gate valve on the return of hot water circuit, then it can be closed until the flow in 22mmm pipe is the same as the rads, Not easy especially in summer when its just hot water. So I tell people if they have a cylinder insulated with foam then it is efficient enough to have hot water on continuous, then it won't be on very often when heating is on. Or on the programmer get the hot water to come on 1.5 hrs before heating.