Radiators not getting heated up random problem

[rameshrs]

When we switch on the central heating the boiler doesnot fire up immediately and the radiators are not getting any heat. But we have hot water throughout the day.If we leave the CH on all thru the day it comes up randomly for an hour for about 3 times in 24 hours. Not sure what the problem is.Sometimes we also feel that whenever we use a lot of hot water(like running a bath or washing up dishes with lot of hot water) after a few minutes the boiler starts and the radiators are heated provided that the CH is on on the timer. We have a traditional potterton boiler with a hot water tank (indirect hotwater heating) and a pump and motorised valve to recirculate water for heating.

Soemtimes when the heating is on if we switch off explicitly it takes more than 30 mins or 1 hr for the boiler to stop. Also the boiler when we touch the outside is really hot when running (is that somthing to worry about??)

We also have a room thermostat near oour landign and a thermostat on the hot water tank.

 

[seco services]

is their one valve or two ?

 

[rameshrs]

There is only one motorised valve.- Landis & Gyr

 

[seco services]

sounds like its sticking and not opening straight away or closing. maybe the spindle is seizing and taking ages for the motor to open the valve.

 

[rameshrs]

what do we need to do to fix it ? Could there be any problem with the Thermostats or the timer switch

 

[seco services]

i wouldn't say the stat as thats only a switch and if the programmer off the stat will have no power.
you could check that when you turn the heating off at the programmer power is lost on that wire

 

[footballfan]

it won't be your stat as it is obviously working, it's just the valve is not opening properley as seco said. if the stat was at fault, the HTG would not be calling at all or turning off at all.

 

[rameshrs]

does that mean the valve is not opening at all or is it slow

 

[seco services]

sounds like its moving slow. is their a lever on the end of the valve?

 

[rameshrs]

yes but the lever doesnot seem to have any tension and it has 2 positions "MAN" and "OPEN". but it moves freely between the two without making any changes in the valve. I cant hear water flow when i move the lever.

 

[seco services]

turn hw and heating off at programmer.
then you should have a power switch maybe in the airing cupboard or near the boiler that will isolate all the power to the programmer etc, turn that off that will reset the valve to its relaxed position.

 

[rameshrs]

ok i will try that.. but the power switch in the airing cupboard has never been on and at this moment while i am writing this the boiler is running and the radiators are getting heated up even though the CH is at the "off" position in the timer, the HW is on "24 hrs" mode in the programmer.

 

[seco services]

is the wall stat turned down ?
turn the hw off does it shut down the boiler.

 

[MANDATE]

Can't see how radiators get hot if CH is off at programmer?.
There should be a wire from programmer CH ON terminal that feeds the room stat. This in turn feeds the 'white wire' of the of the valves actuator head. Power on this 'white' (when stat is turned up) drives the motor/valve up to the mid point position, where it either stays or continues, depending what has been called for and what is satisfied.
If both HW and CH are called for and both not satisfied, the motor/valve stays at mid point. A microswitch is triggered, but a second power source on the 'grey wire' is not live cause HW is on and not yet satisfied.
When HW is satisfied or was not called for, the 'grey wire' would be live and it takes over from where the 'white wire' left off.
This drives motor/valve to CH position and whilst doing so triggers a second microswitch. This microswitch also powered from the incoming white wire, diverts power out through the orange wire to light boiler.
When HW is not satisfied, regardless if the setting is HW or HW/CH the lighting up of the boiler comes from the cylinder stat.
I have experienced 3 problems.
A stiff valve spindle. This meant it was hard work for the motor to overcome the stiffness of the spindle and the return spring.
A faulty microswitch. This meant the motor was fine and valve moved to correct position, but it did not light boiler.
A faulty actuator head. this allowed motor/valve to go to mid point but no further. As soon as HW was satisfied, boiler stopped. This was put down to motor or first microswitch.
A replacement actuator head will cure these problems providing the spindle is not stiff and wiring is correct.

 

[rameshrs]

Seco

Sorry i didnt check the reply while the problem was happening... I will try switching off HW when the next time the boiler fires up without CH on and the radiators get hot.

Also the stat is not turned down.

Mandate

Thanks for your clear explanation.I think according to your list the problem could be the first or the 3rd ,because the micro switch wrong wiring could not have happened as we have not done any repairs and the whole system was working fine last winter. It could be the actuator head or the spindle stiffness..how do we solve this by changing the motor or by changing the valve completely.?