Pumping over/overflowing problem, Y-plan system

13 Jan 2010
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United Kingdom
Hello all

We're having serious problems with our system (Potterton Kingfisher MF Y-plan system) and have called out two heating engineers with no resolution to the problem.

Sometimes when we program the system for hot water, after about 20 minutes, the pipework starts hammering and hot water gushes from the overflow pipe.

At least once when this happened, dirty water has dripped through the ceiling below where the header tank is situated. We have also noticed that the downstairs radiators (where boiler is; pump is upstairs) are so hot sometimes that we can't touch them and can smell paint.

At least once that I know of in the last month (when the problems started) the hammering has started when we were running the CH but *not* calling for H/W. The radiators were scalding hot at this time.

We called out HomeServe (via cover with our bank) and they said the pump needed to be set on high speed, which is all they did. A week later, the problem recurred.

We called a second engineer who said the boiler temperature control was faulty (it didn't seem to work when turned) and replaced this on Christmas Eve. We've since turned down the boiler temperature control but the downstairs radiators are still extremely hot.

We had no hammering since Christmas, until today. The C/H was on and we called for H/W. After about 20 minutes, the hammering started, I turned the entire system off and hot water gushed from the overflow.

Sometimes we run the hot water off but the cylinder doesn't seem to start refilling for several hours after this problem happens and the power shower sometimes actually runs dry (no hot or cold water). Eventually, it will start to refill and the header tank refilling is also clearly audible.

(Note: Just had a shower, 4 hours after I turned the system off. Water was hot and cylinder is now refilling. 22mm pipe out of top of cylinder is still hot to the touch at the cyl exit and still warm a couple of feet up the pipe to the loft).

Hot water runs clear and clean, not dirty in any way.

We had the 3-port valve and heating controls replaced a year ago (detailed on another thread) and were told at the time that the system was originally gravity-fed and has at some point been converted to y-plan.

The more problems we have and the more I read on the subject, the more convinced I get that British Gas (who installed the Potterton 6 years ago for a prior owner) botched the conversion and this is the root cause of the problems.

I'm loathed to keep paying out money for engineers who can't find the problem and wonder whether replacing the entire system with a condensing combi-boiler would be the best option.

Does anyone have any suggestions for what could be causing our problems? 3-way valve stuck in the A+B position?

Thanks in advance
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You have two problems, running out of water is probably a sticking ballcock, the problem with your central heating is a completely seperate issue, as your system was converted from gravity I wonder if they removed the gravity valve, it was used to stop unwanted circulation in the rads when the pump was off, you need to find somebody that knows about central heating systems,

try asking friends or neighbours if they can recommend someone they have used, better than sticking a pin in yellow pages.

Could I just clarify; during the gravity to Y-plan conversion, the gravity valve *should* have been removed - is that correct?

having read some other posts re: pumping over, and given the fact that prior to the work in Jan 2010 (new controls, new 3-way valve, *allegedly* a system flush and installation of inhibitor solution) the pumping over never happened, is there a possibility that there's a blockage somewhere?

We have microbore pipe and I've read that a powerflush can't be done on microbore, that all the rads have to be removed and flushed through. The plumber who flushed the system last year certainly didn't remove the rads.

Thanks in advance
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First a small discrepancy but it isn't pumping over, it is boiling the water and the vent is the release point.

Problem poor circulation or faulty stat, has the phile been pushed in fully, and when it was converted was it changed to the right port if necessary.

Is the pump stopping when it boils.

Some pics showing the conversion around the cylinder would be a good plan.

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