Boiler overheat tripping

[Reman]

Hi All,
First post, from a competent, trained Electrical engineer and ex Service engineer, DIYer and hobbyist.

The boiler Glowworm Ultimate (downstairs kitchen) has suddenly decided to pop the overheat trip.
Never done it before and its not the first time weve run the heating this year or anything, just happened out of the blue.

Pipework around the pump (upstairs airing cupboard) (Grundfoss 15-50) very hot an seems pump is running.
Nevertheless having given it a "tap" and removed the bung screw its definitely spinning.

Ive set the 2 way valve into the manual position
Ive bled all the rads (didn't need doing, no air in them at all)
There's heat getting into the bathroom tall towel rad, but very little in the others upstairs and the downstairs ones are all cold.
The system was drained a year or two ago and inhibitor put in , the rad bleed water is crystal clear
There is water in the loft fill/expansion tank

So after a reset the boiler fires up fine until, again, it trips.

And thats what my wife greeted me with as I came home from a couple of days working away!

So I'm a bit stuck now what to do next.....
My next DIY thought, is that the pump impeller may have failed, though I cant find anything bad about these on the net?
So I'd be grateful for any other input please?

Thanks in advance
Colin

 

[steadyon]

The bathroom radiator might be run off the hot water circuit. If so, it suggests hot water side is OK but CH side has a blockage. My approach would be:

a. Isolate pump, remove head (four allen screws, be ready to stop if isolation valves let by and water starts coming out), check impeller, clean if necessary.

b. If possible, remove actuator head from 3 port valve. See if spindle can be turned easily, but don't forget they are only 15 to 20 degrees of movement open to closed. If doesn't turn easily, replace valve (probably drain down required).

c. If the above fail then likely to be a blockage in the system. Try curtain wire around bends near motorise valve and pump.

If the above fails, probably best to get a professional.

All the above of course should only be attempted if you know what you're doing with mains electricity and go carefully with the water side ready to deal with unexpected leakages.

Good luck

 

[jtsplumbing]

Just because pump is turning doesn't mean impeller is, so could need new pump, or not enough water in system, blockage on cold feed from expansion tank in loft.

 

[Reman]

Thanks for the quick replys.
I'm thinking it is the pump, save for what I've said, as its definitely spinning, hence looking for any other possibilities before I start dismantling it.

As part of the fiddling I've set the boiler stat lower than normal and I'd say it does take longer to trip.
The original problem my wife noticed was no hot water, my understanding is that an oldish system like this still needs the pump to circulate the water into the coil in the tank when heating the water, again pointing at the pump.
Just looking for any other pointers.
I like the curtain wire idea, so might try it, but as said, even from popping rads off for decorating in the past,its a surprisingly clean system, and (bowing to your experience) would that happen so quickly and lose all heat to the rads as mentioned?

 

[rpm]

How old is the pump?

 

[Reman]

How old is the pump?

Id expect about 16 years old, there before we wrere

 

[Reman]

Re the flow;

Using the Immersion heater as I did this morning I had no problem with the flow of hot and cold to the powwer shower which runs direct of the tanks. Does that also discount some blockageness

 

[Dan-HybridHeat]

Re the flow;

Using the Immersion heater as I did this morning I had no problem with the flow of hot and cold to the powwer shower which runs direct of the tanks. Does that also discount some blockageness

Cold feed to fill the heating is fed from a different tank to the shower so doesn't help. Sounds a lot like the pump has had it. What setting is the pump speed on? Try turning it up to max to see if any more heat pushes through.

 

[Reman]

Cold feed to fill the heating is fed from a different tank to the shower so doesn't help. Sounds a lot like the pump has had it. What setting is the pump speed on? Try turning it up to max to see if any more heat pushes through.

Cheers already done that , I can hear the pump motor change speed but no change in the rads.
Theres no reason and I've not had a sudden loss of water through the heating circuit, so as far as it re-filling, it shouldnt need to, as mentioned no air bled from the rads

 

[steadyon]

When you say no air from radiators, presumably you got the usual small jet of water? If so, then not likely to be an issue with blocked feed pipe.

In terms of economically determining what is wrong, and hopefully fixing it, then given your electrical and engineering back ground, I'd still go for:

a. Dismantle and check pump. Replace if faulty.
b. Check motorised valve. Replace if faulty.
c. Check for blockages (while motorised valve off)