Heating Off Rads getting warm

[DEMPSEY1965]

Hi All,
After turning the heating off after the winter I have noticed that the rads are still getting warm. Hot water is set to constant on the timer and the heating is set to off. I will be calling in the experts and I just want to know roughly what is going on here. The system is gravity fed, Greenstar ri boiler, Drayton Lifestyle timer, digistat in the hallway 3 port valve in airing cupboard. Valve appears to be moving freely when heating/water is selected. Also the pump appears to be running all the time even after the boiler has shut off and the only way I can stop it is to turn off the power completely. I have turned off all the rads which was ok but I am a little worried that I will be doing damage just to get the water hot. Now I have turned the heating off completely and using the immersion for the hot water. Any ideas please and thank you for your time.

 

[king of pipes]

I think your getting a little confused here if your hot water is set to constant on your programmer then the pump will run all the time even when the boiler has fired up and gone off , you will not have a gravity fed system with a 3 port valve unless you mean a open vented system fed by a small expansion tank in the loft a greenstar ri boiler is only suitable for a fully pumped system which I think you have all you need to do is program some hot water times into the programmer regards kop

 

[paulusgg]

In many systems, and almost certainly yours, the pump continues to run for a while after the boiler shuts off. The purpose of this pump overrun is to dissipate the heat generated by the boiler. By closing all the rads, unless the system has been provided with a bypass, you're preventing the circulation from returning to the boiler.
Are your radiators fitted with TRV's?
Radiators heating up when only Hot Water is being called for is usually a sympton of reverse circulation.

 

[DEMPSEY1965]

In many systems, and almost certainly yours, the pump continues to run for a while after the boiler shuts off. The purpose of this pump overrun is to dissipate the heat generated by the boiler. By closing all the rads, unless the system has been provided with a bypass, you're preventing the circulation from returning to the boiler.
Are your radiators fitted with TRV's?
Radiators heating up when only Hot Water is being called for is usually a sympton of reverse circulation.

Hi All,
Many thanks for your concern and reply. Yes and excuse my ignorance I have an expansion tank in the loft and the valve has 3 pipes going in so I thought was 3 port, I know it has WMH. What you are saying does make sense except as far as I know has never happened before, I have never had to turn the rads off during the summer months when the heating was off. My water was timed for once a day set from 7am-11pm, so if I set the timer from 7am-9am and then 4pm-11pm this will stop the reverse circulation and is this a normal thing to happen and no need to call in a heating engineer? Valve, timer, stats etc are working normally?
Thanks again

 

[king of pipes]

I would think so and it will save you money on your electric and gas bill running your system as you are the heat has a tendency to creep down the heating return pipework and warm the radiators , you may need to get a single check valve put in the return which comes back from the radiators and into the common return back to your boiler regards kop.

 

[doitmyself]

if your hot water is set to constant on your programmer then the pump will run all the time even when the boiler has fired up and gone off

That is true if the boiler stat is turning the boiler off because the boiler water is up to temperature, not the cylinder water. But if the cylinder stat has turned the boiler off, because the cylinder water is up to temperature, the pump should stop.

Dempsy:
When the problem occurs, does the pipe from the motorized valve to the rads get warm (don't check right next to the valve)? If so, the valve is faulty.

 

[DEMPSEY1965]

Yes, the vertical pipe and the 2 horizontal pipes, left and right are all hot, in full all 3 pipes going in/out of the valve are hot and the pump does eventually stop I have found. I think the valve theory makes sense because this sort of thing has never happened before. I think I may go for the valve change, annoying because it's only about 4 years old. Should I try just the electrical part before getting someone in to drain down? Thanks so much for your time and knowledge.

 

[PhoenixServices]

Get the whole valve changed as it's false economy just changing the head. Just make sure to employ a heating engineer to correctly diagnose the issue, not just tell them to change the valve.

 

[dan_the_plumber]

Yes. Sounds like Motorised valve sticking. If it was working previously it probably won't be a wiring fault. Have valve replaced

 

[Harvest Fields]

I would also say a faulty valve next to the cylinder. Once replaced you should be ok again.

 

[DEMPSEY1965]

I would also say a faulty valve next to the cylinder. Once replaced you should be ok again.

Hi Again
Well I had the whole valve replaced today and I don't know whether things are just settling down but some of the rads appear to be lukewarm, any thoughts on this?

 

[Harvest Fields]

Is there only one valve or two ?

 

[DEMPSEY1965]

Is there only one valve or two ?

Just the one in the airing cupboard

 

[DEMPSEY1965]

Just the one in the airing cupboard

Just strange as I am sure this hasn't happened before, it's not like I have had some work done recently, I keep looking at the controls etc thinking I have moved something. The valve is moving nicely, the timer and stats work are ok, just annoying now!

 

[dan_the_plumber]

If the plumber had to drain the system, which I'm sure he would have. You probably still have air trapped in the system.
There should be a manual air vent in the airing cupboard. It's normally on an upstand pipe just on top of the pump?