Worcester Heatslave 20/25 heating cutting out - extra expansion vessel??

[mchandler]

Hi there, we've had a 20/25 second hand boiler installed, replacing a very old 20/25. The heating cuts out and diverter goes to hot water and stays there, pump stops. I've noticed this can happen after the washing machine fills - the cold inlet tees off very near the boiler mains inlet. I could hear the flow switch flapping as the washing machine fills in pulses. I can get the heating back by simply turning a hot tap on for a few seconds - diverter goes to heating, pump back on and away we go. The heating stops a few times during the course of the day. I've ruled out the room stat (shorted to constant demand). I called Worcester suspecting a flow switch problem. They agreed it needed ruling out so it's just been replaced. But still the heating cuts out. One thing they suggested was the system might need an extra expansion vessels to absorb some pressure in the cold mains incase it's affecting the flow switch. We do have good water pressure here - not sure exactly but it is strong. Any suggestions very welcome... thanks a lot

 

[MarkOil]

If your washing machine is feed by the fresh cold water, that won't effect your system pressure.

 

[Ermintrude]

Oil combi - bad news.... Secondhand oil combi? Are you feeling ok?

 

[SimonG]

Sounds like youve inherited an issue with the second hand boiler. Get the installer back. Or keep chucking parts at it till you get lucky.

 

[MarkOil]

Possibly a faulty stat on the slave tank? Thinking the tank isn't up to temp. worth testing it to see if it's reading correctly. Or throw some more cash at it and just fit a new one, rule that out.

 

[Ermintrude]

I would say its hydraulic failure... Diaghphram / bushes

 

[MarkOil]

Ah I know what the fault is now.................. Worcester Heatslave haha

 

[Bunker]

Sorry buddy, you'll get little sympathy here:

Worcester
Combi
2nd hand

Assuming your installer was OFTEC registered and therefore reputable, get him back. If you didnt use a competent installer then whatever you saved, you will spend on trying to get the thing working. A false economy Im afraid.

For what its worth, I hope you get it sorted.

 

[Killy Bing]

I think the op might have learned why it was second hand.....

 

[mchandler]

Have spent a couple days observing boiler operation: It will happily run and regulate itself for hours, it appears to be a sudden opening of a mains tap (or washing machine feed) sometimes flips it to hot water. Opening a hot tap restores it!
To respond to a few points raised here
* Boiler believed to be operating ok - house was being converted to air source heat pumps. I know we can't be 100% sure and there's an element of risk - but we're only staying in the house another six months and aren't going to spend 2-3 grand installing a new system. We figure a 500 quid like for like replacement boiler that might need a bit of work is still worth it
* Installer is a very experienced Oftec guy - I'm asking around as interested and to try and narrow fault down with him
* I did a couple of years gas work a few years ago and the guys I worked with nearly always preferred Worcester, boilers and tech support. Judging by comments here that doesn't appear to transfer to their oil burners?! Live and learn!

Thanks to those that have offered constructive comments - much appreciated

 

[lame plumber]

pop a hammer arrester next to the wm cold feed

 

[IDCHAPPY]

pop a hammer arrester next to the wm cold feed

This one?