HW Pumping Over

[diynoob]

Hi,

I have an open vernted system with a Glowworm Spacesaver boiler. The same problem happened twice in the last 2 weeks. The HW came on at 6am (a bath was run the night before so there would be no HW in the cylinder at this point). The CH was not on and the HW is timed for 1 hour in the morning.

At 6.40am the plumbing started to make a racket. Very loud clunking and banging. I tuned off the HW timer and the noise stopped. I looked up in the loft and the small FE tank had warm water in it and the vent pipe was hot.

By 6.40am I would have expected the HW to have turned itself off. I thought it might be the cylinder thermostat but its set to 60C and the temperature of the cylinder is 48C when measured with separate thermometers.

Thanks.

 

[gas112]

Fully pumped or gravity hot water pumped heating ?
2 pipes from boiler or 4 pipes ?
Could be the boiler stat thats gone hence the banging and clattering as water in boiler gets too hot and bangs through pipes

 

[diynoob]

It's gravity HW and pumped heating. There are 2 pipes from the boiler.

I don't get this problem with the CH on, even if its on for hours. Only seems to happen with the HW, and only in the morning when the HW runs for a long time.

 

[gas112]

2 pipes then its fully pumped , does sound like boiler stat has gone.
With heating on have you noticed rads are getting far hotter to the touch than before

 

[diynoob]

Heating is on now so I'll see if the rads get extra hot.

 

[stardanny]

Unlikely to be gravity HW, as you have only 2 pipes from boiler. Can you see a metal or white box above pipes which have either 2 or 3 pipes in airing cupboard?
Pic of a airing cupboard with pipework would be good.

Daniel.

 

[diynoob]

OK I misunderstood, yes its fully pumped.

There is no metal white box. Airing cupboard has the cylinder, pump (right way around), 2 motorized valves. The CH vent is just before the feed so it looks OK.

Untitled

• diynoob
• 24 Mar 2014
• 1

 

[diynoob]

Had the CH running for a few hours now and the flow temp at the rads is 60C.

 

[diynoob]

Hmm 68C at the rad nearest the boiler. I'll turn the boiler stat down and see if it responds.

The boiler does come of and on if I adjust the boiler stat. I've had it on max for the last 3 years because its a small boiler (18kw) and a large system (14 rads).

I've set it to 75% now. Not sure why this has suddenly become a problem though.

 

[diynoob]

I'm wondering if the problem is to do with the sequence of events when the HW temperature is satisfied. If the motorized valve closes, but the pump doesn't shut off that would cause the racket and also cause the pumping over of hot water into the FE tanks.

If that theory is correct, woul dit be a problem with the cylinder stat, or the valve, or the pump, or the wiring?