central heating pump delay start

[Paul95]

hi, i have an old style central heating system, boiler, pump, 3 way valve. For ages now i have been trying to solve the reason behind bad knocking of the pipes when the heating starts up. Recently i changed over the pump which had finally packed in, this did not resolve the banging.
What i did realise however was when i connected the pump direct to a wall socket and had it running before i started the heating system i no longer had the banging. I then worked out that when everything was reconnected properly again that the pump was not actually been asked to run by the controller for a few seconds (maybe longer) after the boiler had fired up, i think this delay causes the banging (maybe kettling effect).

My question is: Is it normal to have a delay between the boiler firing up and the pump being asked to run ? and if so what is the reason for this ?

 

[AGAS]

boiler ?

 

[Dan Robinson]

boiler ?

It's a white one you silly.

 

[John D v2.0]

No it's not normal, usually the other way round. And the pump usually runs on after the boiler stops. Perhaps the pump and boiler are connected to the control system the wrong way round?

 

[stem]

Perhaps the pump and boiler are connected to the control system the wrong way round?

Whilst your comment about the overrun is correct, the pump and boiler wiring could not be transposed. If a boiler needs a pump overrun, then it is provided with dedicated pump wiring terminals and contains the timer circuitry for the pump. For what you describe to happen is impossible as the pump doesn't have any timer function or terminals that could be used to control the boiler.

 

[John D v2.0]

Whilst your comment about the overrun is correct, the pump and boiler wiring could not be transposed. If a boiler needs a pump overrun, then it is provided with dedicated pump wiring terminals and contains the timer circuitry for the pump. For what you describe to happen is impossible as the pump doesn't have any timer function or terminals that could be used to control the boiler.

Ah right fair enough I thought he might have an external unit controlling both. If not then I agree it's not possible.

 

[D_Hailsham]

hi, i have an old style central heating system, boiler, pump, 3 way valve.

What is the make and model of your boiler?

 

[Paul95]

The boiler is a thorn emi appollo 4.0, the controller is a sunvic sp100, the pump a grudfos.
Yes all very old equipment i know but so reliable, whilst other friends and family have shelved out fortunes for replacements, repairs and breakdown cover (for better efficiency!) over the years, my boiler just keeps going without a problem (except for this dam banging on start up)

 

[Ihavenojob]

Sounds like the pump over run stat is playing up. It's fitted at the bottom right inside the boiler, you will need a registered engineer for this job

 

[D_Hailsham]

Sounds like the pump over run stat is playing up.

Beat me to it!