CH Pump Problem

[Johntheo5]

Regarding that service valve, I remember a plumber while ago said it's bypass of some sort, guess to protect boiler from overheating. How is this valve set? I just put it back roughly where it was, does closing it further will provide more heat to the rads?

Your system looks like S plan with motorized valves to the CH and HW cylinder (coil) heating so when the CH or/and HW heating demand ends then both valves close and the pump should run on for a few minutes (to cool down the boiler heat exchanger) but there must ba a path for the water to circulate around, a automatic bypass valve (ABV) is often used but your's just has a manual valve in the bypass pipe between the flow&return pipes?, suggest, while with a constant boiler demand just shut this fully for say 15/20 minutes to allow the pipe to cool down, then just gradually open it very slowly until the pipe starts getting hot. But check that your system does actually run (overrun) the pump for a few minutes when the boiler shuts down, opening that manual bypass valve a small amount shuld have no effect on your rad/cylinder heating. How many rads??.

 

[fixitflav]

SORTED!!!

I hope you've kept the old pump. If so why not dismantle it, easy to do on the bench, and tell us if there are any obvious faults, eg blocked impeller.

 

[yartin]

I hope you've kept the old pump. If so why not dismantle it, easy to do on the bench, and tell us if there are any obvious faults, eg blocked impeller.

Yes I have kept the old, will dismantle may be in the weekend, will post photos.
According the installer, implied it was dead, 240v was getting boiler kicking but nothing happening, will find out hopefully when dismantled.

 

[Hugh Jaleak]

Have known a Pump to fail on a couple of occasions, shaft was spinning but the Impeller had parted ways, so no water was being moved. Would hazard a guess that's what's happened here.

Service Valve in this instance acts as a Bypass, so should both the Motorised Valves close, there is still an open path for the water to circulate and the pump is not pushing against total resistance. Cracking it wide open and the water will take the easiest path, through the Bypass rather than around the system. Closing it down forces the water around the system to the Radiators.

 

[yartin]

Have known a Pump to fail on a couple of occasions, shaft was spinning but the Impeller had parted ways, so no water was being moved. Would hazard a guess that's what's happened here.

Service Valve in this instance acts as a Bypass, so should both the Motorised Valves close, there is still an open path for the water to circulate and the pump is not pushing against total resistance. Cracking it wide open and the water will take the easiest path, through the Bypass rather than around the system. Closing it down forces the water around the system to the Radiators.

Would an automatic bypass valve do a better job? it's suggested by @Johntheo5 in post #61 above.

 

[yartin]

Your system looks like S plan with motorized valves to the CH and HW cylinder (coil) heating so when the CH or/and HW heating demand ends then both valves close and the pump should run on for a few minutes (to cool down the boiler heat exchanger) but there must ba a path for the water to circulate around, a automatic bypass valve (ABV) is often used but your's just has a manual valve in the bypass pipe between the flow&return pipes?, suggest, while with a constant boiler demand just shut this fully for say 15/20 minutes to allow the pipe to cool down, then just gradually open it very slowly until the pipe starts getting hot. But check that your system does actually run (overrun) the pump for a few minutes when the boiler shuts down, opening that manual bypass valve a small amount shuld have no effect on your rad/cylinder heating. How many rads??.

I had 8 rads when moved in 2002 and all was fine but after ground floor extension became 12 rads had issues heating the rads in the extension, been balancing them and it's ok, kept same heat only boiler 18KW.

 

[yartin]

.

 

[Hugh Jaleak]

So why did the first gas engineer open the service valve fully?!

I suspect because he doesn't know what he's doing!

If I go back to your original post, your description of the issue has all the hallmarks of poor circulation, and I'd wager the grinding noises were the Pump failing. Boiler will fire and heat the water within the Jacket, but as that water isn't getting moved, it quickly gets to temperature and so the boiler shuts off. Over the next 30mins or so that heat will dissipate sufficiently for the Boiler to fire again briefly.

System relies totally on the Pump to keep moving the water through the Boiler as it absorbs the heat being put out by the burners, if pump isn't moving the water, this is the result.

 

[Johntheo5]

Yes, why did the chicken/engineer cross the road?, who cares, the system is now working.
A ABV will only work to a fashion in these A Rated pumps because as is well known, none have true fixedspeed/constantcurve modes, the UPS3 is the very "worst" one in this regard, see below. On the choosen fixed speed II, the head only falls by ~ 0.15M between no flow and almost 0.8m3/hr, 13.3LPM which will satisfy the full flow demand of a 14kW system at a dT of 15C. You are as well off IMO with that throttled service valve if you set it up as I suggested. A constant bypass of say 2.5LPM will only raise the boiler return temperature by 2 to 4C. But first, check, again as suggested, that the pump does overrun for a short period when the boiler shuts down.

 

[yartin]

I emptied the header tank last week, is it a good idea to add 0.5L of the Sentinel x100 to the system? Guess taking off 0.5L or so water from header tank replacing it with the inhibitor will do the job?

 

[Hugh Jaleak]

Ideally, draw enough water out the system to empty the F&E Cistern, tip the whole bottle of X100 in, and then allow Cistern to refill. It will get drawn into and around the system faster.

 

[yartin]

I took off the 4 hex keys, what to look for?

 

[Johntheo5]

You should be able I think, to remove the impeller assy. where arrowed.

 

[yartin]

I took off the 4 hex keys, what to look for?



View attachment 402633

I managed to remove the impeller, there is no blockage in the veins BUT the fan is not turning freely meaning the grinding noise I heard last time was working was when internal components got damaged?! photo below, it is repairable with new impeller from Ali express for under £40.

 

[yartin]

You should be able I think, to remove the impeller assy. where arrowed.

I looked on you tube and there was a vid.