Hot water pump problem. Question for the plumbers?

[Jonny69]

Could be one for the plumbers here but anyone with experience with their heating and hot water might be able help me. The hot water pump is getting stuck on. We've got an old conventional system with hot water cylinder. The hot water is set to come on between 5:30 and 6:30, but the pump isn't switching off. It'll run all day if I just leave it but gets incredibly hot, presumably because it's pumping against a closed valve. So I guess I need to find out if this is a serviceable item or if you have to replace it, or if there's a controller that's at fault.

Some info that might help:
-I replaced the central heating timer from an old mechanical one to a digital one. Direct swap and appears to work fine. Everything worked ok for the first 6 months we lived here.
-There's a power switch in the airing cupboard that appears to supply power to the pump (not the immersion heater). If I switch off the pump here, sometimes it clicks the pump off and it'll stay off and go back to working correctly. Sometimes it'll stay off for one cycle and stick on again next time the hot water comes on. Sometimes the pump just comes back on again when the power comes on and stays on, like it's doing at the moment. I noticed the switch in the airing cupboard also switches off the central heating timer (which is downstairs with the boiler) and I don't know if that's correct or not.
-You'll probably want to know what type of system it is. It looks identical to the 'conventional system' diagram on this page: http://www.diydoctor.org.uk/projects/boilers.htm

 

[Nightglow]

What boiler?, might be a pump,overrun switch in boiler
But, more like faulty port valve, little switch inside it, is faulty, & not switching pump off.

Some have replaceable motor & actuators, other you completely replace.

 

[Jonny69]

It's a 1990's Ideal, a real old hunk of ****. Theoretically, if it was a switch inside the boiler, if I were to switch the boiler off it should shut the pump off (assuming it's not a relay stuck open). I'll give that a go and see what it does.

So the port valve, is that part of the pump or one of the two valves that switch on/off the flow of water to the heating and hot water? Sorry for the dumb questions, I'm new to this. It would be great if it can be replaced without taking the pump off, because that means a lot less work

 

[Jonny69]

Pic:



Is it possible to open this one or is it a replace job? Looks like replacement might not be as much work as I anticipated, since there's an isolator top and bottom. Assuming those crusty old isolators hold out, not having to drain the system is a massive bonus!

 

[Nightglow]

If you put flat blade on the end of a screwdriver on the pump, & then press your ear on the handle of the screwdriver. You should hear the whirring of the pump.

I suspect port valve, but without testing pump & valves, I can't 100% sure, it' not the pump that has failed.

Sometimes they will not shut of, but continual to run, due to component failure.

 

[Attu90]

Im no expert but im sure your port valve it the silver box on the top of your pic but it could also be the white box to the left of the pump.

Are the both port valves ?, it looks to me as though its got 2, 2 way valves instead of 1, 3 way ? ....like I said im no expert but I have had to change a 3 way valve on my system a while ago.

 

[Steampunk]

Might be the diverter valve, especially if you can feel/hear the pump running. Newer ones have replaceable parts. Older ones you have to replace the whole thing.

 

[Jonny69]

The two white boxes control the flow through heating or hot water system. From what I can work out, heated water from the boiler comes in to the bottom of the pump; the top white box allows or shuts off the flow into the hot water coil; the bottom one allows or shuts off the flow to the radiators. So could one of those two be causing this? I think I'm struggling to work out what controls the pump. What actually switches it on and off? Is it temperature controlled by the boiler, pressure controlled by either of those two valves in the white boxes, or is it switched on and off by the central heating / hot water timer?

 

[Attu90]

The valves will turn the pump on and off via the electric circuit, its strange ( to me at least) that they didn't just use a single 3 port valve instead of 2 x 2 port valves, I guess there must be a reason for it ?

Anyway, yes if one of those has failed it could be the reason the pump is not turning off.

Some makes of valve you can just pull the head off (the white part) and replace it where as others you have to replace the whole valve meaning draining the circuit.

One tip if you do it yourself, draw a detailed diagram of the wiring ... I didn't , it took me ages to figure out which wire went where.

 

[Jonny69]

The valves will turn the pump on and off via the electric circuit, its strange ( to me at least) that they didn't just use a single 3 port valve instead of 2 x 2 port valves, I guess there must be a reason for it ?

Probably because everything in this house has either been bodged, done by someone who didn't know what they were doing or done on the cheap

Anyway, yes if one of those has failed it could be the reason the pump is not turning off.

Ok, I'll find a way to check them. So from what you've said, the central heating timer fires up the boiler and opens the valves, and the pump kicks in automatically?

One tip if you do it yourself, draw a detailed diagram of the wiring ... I didn't , it took me ages to figure out which wire went where.

Noted

 

[Jonny69]

Ok, I think I might have found the problem but I'll have to wait a few days to check. There's a little plastic lever on the side and what looks like a button on the back and they're both connected together under the motor that opens and closes the valve in the pipe. I'm guessing they are there so you can manually open the valve to test the pump. I'd seen it before but it was jammed. I just freed it off and now the lever and button will open and close the valve and trigger the pump. It's all nice and free but the plastic mechanism feels like it might be broken or jumped off the spring because it sticks in the open position. The one on the central heating valve is definitely broken because it's missing the button bit at the back.

I'm going to wait until the pump next sticks on and see if the plastic mechanism is in the position where it gets stuck. If it is, I'll just take it off for now and think about replacing the top bit of the valve at some point because it looks like it comes off without the valve itself.

Thanks for the help chaps - invaluable stuff