Boiler only heats water for 45 seconds at a time

[cjyoung]

Hi all,

I'm a complete novice when it comes to plumbing & central heating systems so please bear with me...

We have a Glow Worm Flexicom 15hx boiler (located in the kitchen) which was installed just under four years ago. During the time we've had the boiler we've had a number of occasions when we've experienced a loss of hot water and central heating. We symptoms always seem to be the same: the boiler appears to operate correctly but when the burner comes on the indicated temperature rises quickly from ~45 deg C to the required temperature of 70 deg C at which point it shuts off. The burner is only active for about 45 seconds which, I guess, is not really long enough to heat the water properly. I'm not sure how reliable the temperature readout actually is. The net result is that the radiators either don't heat up at all or become lukewarm and the same is true of the water in the hot water tank. We often find that the pump gets very noisy after about 15-20 minutes of operation as well (this may or may not be related).

We've had the original installers out a number of times and have had a replacement pump and new hot water tank as a result. Both 'solutions' sorted the problem for a period of time but now it's resurfaced again. Does anybody have any suggestions as to what the cause of the problem could be? I'm reluctant to have to call the installers again because every time we do it seems to cost hundreds of pounds without actually resolving the problem.

In case it makes any difference I've bled all the radiators (two upstairs, two downstairs and one towel rail in the bathroom) and there is no (apparent) air in any of them. That's about the limit of my 'expertise' I'm afraid!

 

[quality]

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[Destroyer2813]

Sounds like the heat aint getting away from the boiler quick enough is the pump excessivly hot maybe gone again. Is the system water dirty? or the ballvave in the header tank stuck causeing the pumps to burn out?

 

[cjyoung]

Thanks for your replies. The pump gets hot to the touch but I was under the impression that that's normal (perhaps not?). I haven't checked the header tank but will do so tomorrow when I can get my step ladder out to get into the loft. The water that came out of the radiators did not seem to be particularly dirty. We do live in a hard water area so I suppose it's possible that the pump has simply worn out but I would have hoped to have got more than a couple of years out of it.

 

[kozak1968]

try winding the bypass in a little.

 

[Mike Jackson]

try winding the bypass in a little.

And achieve what? The problem is obviously a lack of flow through the boiler possibly caused by a failed pump, low system water or an airlock.

 

[Destroyer2813]

The pump should be hot to the touch but not excessivly hot, try taking a large flat bladed screwdriver to the bleed point of the pump and see if the impeller is spinning

 

[kozak1968]

could be the resistance through the system. If the bypass is open then it can short circuit. Had it on a betacom

 

[Halesowen1]

I reckon its the pump, possibly running dry etc due to incorrect pipework, this may explain why it works for a while when changed. As it would have been bled then, but after a while it is gathering air and running dry. Seen this a few times.

 

[warrington]

what code you getting from boiler when it shuts off?

 

[cjyoung]

I reckon its the pump, possibly running dry etc due to incorrect pipework, this may explain why it works for a while when changed. As it would have been bled then, but after a while it is gathering air and running dry. Seen this a few times.

We've been in the house for six and a half years now and have realised during that time that there's obviously been a fair amount of DIY work done previously. Some of the pipework was re-done when the boiler was installed because the fitters said it hadn't been properly. I suppose there could still be pipework elsewhere which is also in need of re-work. Unfortunately, I wouldn't know whether it's right or not and rely on the professionals to tell me.

 

[cjyoung]

what code you getting from boiler when it shuts off?

Sorry, I should have been clearer with my original post. The boiler isn't reporting a fault code - what I meant by 'shuts off' is that the burner stops as expected when it reaches the target temperature. It's just that it gets there really quickly. Under normal operation our boiler takes about 4-5 minutes to get the water from 45 deg C (-ish) to 70 deg C but at the moment it claims to be doing it in about 45 seconds.

One thing I have noticed is that just before the burner stops when it's not functioning correctly the temperature readout jumps temporarily to 99 before dropping back to 70. I'm not sure whether this is significant or not or just a 'feature' of the boiler. Could it indicate a faulty thermostat or temperature sensor within the boiler perhaps?