Radiators cold when boiler fires up on automatic on/off settings

[wongo]

My boiler (Potterton Suprima 60) fires up OK but the radiators stay cold. It happens when the heating controller is on automatic on/off time settings. The pipes close to the pump (a 20+ years old Grundfos) and Honeywell (new) diversion valve do get hot though. The controller is a Sunvic SunPro2000 installed new last July. However, when I use the manual Advance buttons to switch the heating on I do get heat on the radiators.

Nothing had changed since last July when a new PCB kit was fitted. Everything was working fine until the last few chilly days when I decided to on heating.

Could the problem be the pump or the Sunvic ?. I have the radiators bleed.

 

[doitmyself]

The pipes close to the pump (a 20+ years old Grundfos) and Honeywell (new) diversion valve do get hot though.

Is the pipe after the valve hot? Check as far away as you can.

when I use the manual Advance buttons to switch the heating on I do get heat on the radiators.

So the boiler is OK. The problem must be with the control system; possibly the Sunvic.

Do you have a multimeter (and know how to use it)?

 

[wongo]

I had the boiler fired up at 16.30 set programmed time. After 30 mins the radiators remained cold. As to the Honeywell valve,the pipes marked AB and B became vey hot but the one marked A remained lukewarm.

I then switched off both CH + HW using the Advance buttons, waited 10 mins an switched them back on. I got the boiler fired up and the radiators began to warm up. After 30 mins the radiators got hot. All the 3 Honeywell pipes A, B & AB got very hot. The pipe from the pump also got hot

 

[doitmyself]

Turn heating ON and hot water OFF.

Do the rads get hot?

Turn the Hot water ON and turn cylinder thermostat down.

Do the rads get hot?

The pipe from the pump feeds AB on the valve.

 

[AWheating]

Who changed the motorised valve? Did it ever work correctly with the new valve?

 

[wongo]

AW, yes the Honeywell valve has been working ever since it was fitted brand new last September.

 

[wongo]

DIY, when I manually fired up both CH and HW this afternoon the radiators did get hot and even when I off HW.

It was different when the boiler fired up at set times this morning and this evening. I set both CH and HW to come on/off same times. The radiators stayed cold even after 30 mins. But the moment I off HW I could hear a splash sound in the boiler and the radiators started to heat up. I don't know what you can make of this. The issue of cold radiators only occurs when the boiler fires up on set on/off times. It is a recent issue.

 

[doitmyself]

Sounds like a faulty Sunvic programmer.

A multimeter would be very helpful.

 

[wongo]

Got the Sunvic controller replaced by the seller today. Now everything is working as it should be. So the issue was with Sunvic controller which lasted only 7 months from new.

 

[doitmyself]

Got the Sunvic controller replaced by the seller today. Now everything is working as it should be. So the issue was with Sunvic controller which lasted only 7 months from new.

They don't have a good reputation.