CH boiler over-run/pumping over

corcaigh1

Hi all,

Having an issue with a gas boiler pumping over…


History as follows -

• Home is 30 years old running an open vented F&E system. 9 Radiators.
  
  
• Potterton Suprima 50l (2004) serviced and running very well.
  
  
• Climote controller and 3 x Zone valves fitted approx 2 years ago.
  
  
• Recently was in the attic and noticed quite bad condensation, noticed the vent pipe from the CH was pumping over into the F&E tank. Eventually figured out it was only pumping over when a single zone was turned on i.e upstairs heating only.
  
  
• Had issues with cold spots on downstairs rads so ran X400 for nearly 4 weeks and drained the system, decided to remove all effected rads, cleaned and hosed them out thoroughly until they ran clear. 30 years of sludge was bad! Cleaned F&E tank spotless, refilled the system and added X100 inhibitor. I think that eliminates any chance of blockage/obstruction in the system as all rads heat perfect now with no cold spots.
  
  
• The boiler is still pumping over on a single zone and as normal over-runs(but pumps over) for approx 2 mins when the CH is timed off. If two zones are put on together i.e upstairs and downstairs the boiler does not pump over…
  
  
• An automatic bypass valves is fitted to the immersion pipes upstair in the cubby, I thought that may be the issue so tried resetting it by closing it fully to 0.7 and then turning off all the rads except one for the purpose of backing off the ABV until flow through…
  
  
• Turned on the upstairs and downstairs heating and the vent pipe(blue) immediately got hot (system pumping over) the (green) pipe also got hot in the lower part but not in the upper part after the compression fitting and then the (orange) pipe got hot within about 3-4 mins with the ABV still fully closed, should that not be the case?

Im confused as to the operation and location of the auto bypass valve, its there to prevent pump-over? is it working and fitted in the correct location, direction?

Pics below of pipework above boiler and cubby for reference…

K.Flyer

If your heating system has a feed and expansion with an open expansion pipe from the heating system, and a separate feed pipe back to the system, then an auto by pass valve will not prevent "pitching" of water through the expansion pipe over the tank. It is not the purpose of the abv to prevent pitching.
It would appear that your system is still a fully open vented system, albeit that it is zoned.
My suggestion would be to either fully seal the system, or have it changed to semi sealed if it's an older system and have the tank acting as a feed only.
It's important to get someone who knows what they are doing to rectify this for you.
Pump speed adjustment might work, but that may cause zones not to heat up as quickly as usual.

corcaigh1

K.Flyer wrote: »

If your heating system has a feed and expansion with an open expansion pipe from the heating system, and a separate feed pipe back to the system, then an auto by pass valve will not prevent "pitching" of water through the expansion pipe over the tank. It is not the purpose of the abv to prevent pitching.
It would appear that your system is still a fully open vented system, albeit that it is zoned.
My suggestion would be to either fully seal the system, or have it changed to semi sealed if it's an older system and have the tank acting as a feed only.
It's important to get someone who knows what they are doing to rectify this for you.
Pump speed adjustment might work, but that may cause zones not to heat up as quickly as usual.

Yeah its defo something ill have to get a heating plumber to look at...



I've tried pump speed 1 and the boiler doesn't pump over but some rads are not heating up fully. I thought the ABV prevents pump over by allowing flow when the system is restricted by only having one zone on.



Cheers for that info "K.Flyer" ��

K.Flyer

Under normal circumstances the auto by pass is there to create a flow circuit so that the pump is not pushing against a closed pipe when the zone valves close. It's spring loaded to open from the pump pressure.
The flow of water from the pump will want to follow the path of least resistance, in your case that is up through the expansion pipe creating a circuit through the tank.
Whoever put the auto by pass onto the system should have known this if they were familiar with heating systems and how they work and should have made the appropriate alterations to the pipework.