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)

 

[kris]

Defo a circulation problem of some kind. If pumps fine then somethings causing the heated water not to move .

 

[Gary59]

Had the same problem more or less 2 weeks ago, removed blockage in pipe work by connecting garden hose to CH return pipe, another hose to flow pipe to eject water away and back flushing each rad in turn while rest screwed down. Lot of crud removed and heating worked fine after.

Make sure it is not the pump first thou.

 

[Reman]

.

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).
icity and go carefully with the water side ready to deal with unexpected leakages.

I want ready to get wet tonight so I'll look at the pump I'm the morning.
I did pull the 2 way valve apart though.
`Thanks for the 15-20 deg advice. If i'd not seen that I'd probably thought it jammed and unjammed it very roughly and broke it!
From what i can see though, there is no OFF its either A or B so even if this was jammed it would not be "shut", it will still let water pass one way or the other so should not cause the problem I have?
I'll poke at the pump in the morning

 

[Reman]

Looking further at the valve spec its actually 3 way (4073A) I believe so you can have , water, heating or both. With this in mind and the fact that the pipework is getting plenty hot on both outlets I've convinced myself for now that the chance of it being totally blocked in any position is slim, therefore I'm putting it back together for now. I also ran the boiler for a considerable time with it on its lowest temp setting before bed, without it tripping the overheat, so next stop the pump I think?

 

[Reman]

We were all in the right area, but I needed to be sure! Apart from anything else the pump was a pig to get at, due to having had built in wardrobes built around the old airing cupboard location, so needed to be sure before I got on it as I'm not very bendy!
Pump bought stripped the head unit off to save disturbing the piping, re-wired, and of it jolly well went

Good work and thanks to the to the UKP collective
:coolgleamA:

 

[Subby]

I've had a couple of older gloworms overheating and a powerflush has sorted the problem. maybe the system would benefit from a bottle of x800 for a day or two then a full cold and then hot flush with all zone valves hooked open, and the tank in the attic cleaned thoroughly with sponges, buckets, wetvac etc, and re filled with a decent inhibitor x100 etc

 

[Reman]

Well theres an update to this, it worked perfect on plain water for about 2 weeks ,so I thought I'd finish the job with a flush of cleaner (as suggested) to remove any other issues mentioned before I put it all back together for the winter.
So I drained it down, dropped in the F3 cleaner and ran it for a few days, but found that occasionally it was tripping the overheat on first timed switch on. Reset then ran OK, I guessed it had perhaps got a bit of air in the boiler circuit. But put up with it for the few days.
Drained it down, refilled for the first of 2 rinses. First rinse worked perfect for a couple of days, second rince for last two days its been tripping from cold start.
I can only guess that it needs a super bleed, so would not worry till its got inhibiter in it and bleed super thoroughly.
Anyway thats where we are BUT. In the process of doing this the drain above the boiler has got increasingly leaky, having had to shut it tighter and tighter to keep it from dripping. So tonight I drained it and to put the inhibitor in and during filling the train leaks and I can't stop it!!
So I've had to abort and drain down again and I'm now scratching my head wondering how I get out of this one!
Biggest problem is limited access without tearing the kitchen apart as you should a see from the pictures. Only by wafting my phone under the coving could I get this shot.
So the question is, can you identify the options from the fittings used?
I wondered if I could cut off this drain and compression drain, but I'm not sure that the size is right or there is enough shank to do that? Thanks in advance, I'm seriously in the dog house!!

 

[jtsplumbing]

Just buy a new drain off cock and replace innards or just replace washer

 

[gassafe]

As above.. It looks relatively modern, so should only need new innards from replacement valve... Just make sure the washer comes out whole & has a good seating face before fitting the new one!

Sometimes they seal up once ther warm as the runner reseats... I would try it on hot water only & crank the stat up!!

 

[Reman]

Thank guys , been on the desk job too long!
Washers fitted job jobbed.
Tonights mare is getting the boiler to run without tripping the super over heat theres obviously no water got to it and the pump is pulsing (yes bled that) so I'm in the middle of another drain and re-fill again. I think i must have been really mean to someone recently!

 

[jtsplumbing]

The F3 cleaner is no good for what you are trying to do, you need F5 heavy duty cleaner, leave in system for at least a week and run on high temperature for best results

 

[Reman]

It is done!
Finally got the boiler bled enough to not overheat, (it took another top half drain down band refill) ran up and more importantly fired up on the timer this morning without tripping and again this evening too. So fingers crossed you won't hear from me for a while.
Thanks again