Strange zone valve and pump behaviour..

[dpravo]

I have an S plan system and over the last few days i've noticed strange behaviour which I hope someone can help diagnose..

When the hot water comes on (typically on a timer), the h/w zone valve opens, the pump starts and then the boiler fires up.. after some time, with the hot water still 'on', the zone valve closes and the pump turns off. Then after some more time the zone valve reopens, the pump starts and the boiler fires up.. then the cycle just repeats.

What used to happen was that once the hot water came on, the zone valve would stay open and the pump would run the entire time the h/w was on.. with the boiler firing up intermittently to keep the hot water cylinder hot.

Can anyone advise what might be causing this change if behaviour? Thanks in advance for any advice!

To add to this ( and I hope its not related ) i did have a replacement pump fitted a few weeks back.

[Someone-Else]

i did have a replacement pump fitted a few weeks back.

............and when did this problem start? and who changed the pump? (Plumber, heating bod, you?)

[dpravo]

The problem started about 2 weeks after the pump was changed, by my usual plumber/heating engineer who has been working on my house for years.

[Someone-Else]

I would suggest you ask him, did he do ANYTHING else?

[dpravo]

Great suggestion, thanks. Yes he also replaced a degraded o-ring on a Magnaclean filter.