I need some theory explainng on radiator flow

[peter lanky]

I had a new boiler installed in August, which I have only recently started using for heating the house, previously only requiring hot water. The installation included power flushing of the radiators. All radiators except one have thermostatic valves. The boiler is a Worcester Bosch system boiler.

Now one of my radiators is nice and hot at the top, but tepid at the bottom, but more relevant to my lack of understanding, the water outlet from the radiator is also tepid. This is where I'm confused because surely to get the top of the radiator hot, hot water must be flowing into it and therefore must have to flow out. So how can the outlet be tepid?

So having had the system flushed only 3 months ago, what else could be causing the bottom of the radiator to be tepid?

 

[Nostrum]

Depends how much water is flowing through the radiator. Get them back as they've not finished the job properly.

 

[petercj]

I had a new boiler installed in August, which I have only recently started using for heating the house, previously only requiring hot water. The installation included power flushing of the radiators. All radiators except one have thermostatic valves. The boiler is a Worcester Bosch system boiler.

Now one of my radiators is nice and hot at the top, but tepid at the bottom, but more relevant to my lack of understanding, the water outlet from the radiator is also tepid. This is where I'm confused because surely to get the top of the radiator hot, hot water must be flowing into it and therefore must have to flow out. So how can the outlet be tepid?

So having had the system flushed only 3 months ago, what else could be causing the bottom of the radiator to be tepid?

If that radiator is the last in line, it could be that it's not getting enough hot water to heat it right through - hot water does tend to rise, not sink.

Might be that the radiators need balancing to get more hot water to the ones farther down the line. Try turning off two of the hot radiators and see if that makes a difference. Also, take the top off the TRV and make sure the pins not stuck.

Info on balancing:-

http://www.homebuilding.co.uk/advice/DIY/how-balance-radiators

 

[peter lanky]

That sounds like the solution. I'll give it a try.

 

[DirksPlumbing]

Re: I need some theory explaining on radiator flow

That sounds like the solution. I'll give it a try.

Just to ask, the Thermostat is fully open and the room is not at the desired temperature?
Otherwise this behaviour would be perfectly normal for this time of the year.
Especially if the radiator is a fairly large one and/or the room is well insulated.
A noticable difference between the temperature coming in and going out is not only wanted but necessary for the function of your heating.
Otherwise if it is outwith normal behaviour I often find radiators being overbalanced or simply someone forgot to open the return valve after doing some work to the system.

 

[peter lanky]

The thermostat is part opened (3 out of 5), but the room seems cooler that the others. I rarely have the boiler on longer then 90 mins at this time of year, as I don't let the house get too warm. The thermostat is set at 18 degrees.

I've also tried to check the order that the radiators heat up and found it impossible. That seems to get warm almost together. One thing I've noticed is that some radiators are warming first at the thermostat end, and others at the lockshield end. I did have the thermostat valves fitted around 5 years ago, but these were fitted on the same side as the wheelhead valves which were installed when the house was built.

 

[PlumbBobBob]

that could be your problem. not leaving the boiler on long enough combined with radiators out of balance.

 

[peter lanky]

We've always done it like that. 7am-8:30am, 3:30pm -5pm, 6:30pm - 8pm or there abouts. However, I'd be interested to know if there is an optimum way of operating a boiler. Somebody suggested leaving it on all day and letting the thermostat regulate the temperature, but others have said that is not the best way to do things.

 

[TBServices]

We've always done it like that. 7am-8:30am, 3:30pm -5pm, 6:30pm - 8pm or there abouts. However, I'd be interested to know if there is an optimum way of operating a boiler. Somebody suggested leaving it on all day and letting the thermostat regulate the temperature, but others have said that is not the best way to do things.

Depends on the house, how long it takes to heat and how long it retains that heat tbh.