The other day most of the radiators downstairs were either luke warm or cold. Had a look online and I think it is the hot water pump.
Left it til today, I wanted to make sure it wasn't stuck and was spinning freely. Isolated it electrically, took the bleed screw off, spun the impeller, put the cover on and turned the CB back on. And nothing. The boiler won't fire up the when selecting CH to on from the controller. The pump isn't running, all quiet.
If the pump is bust, would it stop the CH from working completely?
Could it be the pump or something else?
By pump I mean this sort of thing
www.made-in-china.com/showroom/westone1/product-detailnqpJmLhDVlkb/China-Hot-Water-Circulator-Pump-UPS25-40-180-.html
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Yes the boiler works fine for hw
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...it would help to suggest possible causes if you described the type of system you've got.
From your symptom description, I'd guess a combi boiler, but it might be fully-pumped with a three-port valve, or even part-gravity.
The pump not working in any of those circumstances would likely cause a lack of heating, but the cause of it not doing so could be other than actual pump-failure.
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It's a gravity fed system. So a cold water tank in the loft and the hot water tank is in the airing cupboard, as is the hot water pump.
Last edited by: sooty123 on Fri 18 Nov 22 at 15:45
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Does the pump run OK with the CH switched off and only HW on?
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>> Does the pump run OK with the CH switched off and only HW on?
>>
No, but I'm not sure if it did before. I can't say I ever listen for it on HW only.
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....in that case, if the pump is not running when CH is on, then it is either borked, or the switching circuit is non-functional.
Probably the only reliable way of testing is to measure for the presence of current at the pump terminals (or a nearby junction box) when the CH function is switched on and the (any) thermostat is turned up high enough to fire things up. Lack of volts means it isn't the pump.
If you have hot water, I'm assuming (with a gravity system) it's relying on the boiler thermostat to trip the boiler out out once the hot water is to temperature. As you say the boiler won't fire up when CH is selected, is the boiler still hot from (gravity) water heating (which would keep the boiler tripped-out)? If you're selecting CH with a cold boiler and the boiler isn't firing up, the switching arrangements are much more suspect than the pump.
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We had a fault with ours where a dry joint in a circuit board on the boiler meant the pump wasn't 'called on' when either CH or HW was demanded.
Very quickly indeed the water in the HW circuit (ie indirect coil in the copper cylinder) boiled and the boiler overheat operated.
I'd expect Sooty's to do the same if the pump is borked unless it's a direct thermosyphon.
My guess is a switching issue on the CH side.
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Lack
>> of volts means it isn't the pump.
>>
That's what I was heading towards. Seems odd it's just dead completely.
>> If you have hot water, I'm assuming (with a gravity system) it's relying on the
>> boiler thermostat to trip the boiler out out once the hot water is to temperature.
>> As you say the boiler won't fire up when CH is selected, is the boiler
>> still hot from (gravity) water heating (which would keep the boiler tripped-out)? If you're selecting
>> CH with a cold boiler and the boiler isn't firing up, the switching arrangements are
>> much more suspect than the pump.
>>
I was just trying that as I read your post. I'll drain some HW off and see if that does anything.
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One of the diverter valves is buzzing, which I've not heard before.
If that is stuck in the wrong position, could it be that?
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...we crossed posts.
I suspect you're not gravity hot water, but fully pumped.
Diverter/three-port valves are likely in most such setups to have switching functions. If they don't move, the appropriate circuits aren't completed.
If the motor is defective, it's possible you have a lever on the unit that will manually shift the valve (and complete the appropriate switching). If the valve itself is stuck, then you can't test it via this, but it is odds-on that that's your problem.
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>> I was just trying that as I read your post. I'll drain some HW off
>> and see if that does anything.
>>
...if it's gravity hot water, it won't have an immediate effect on the boiler as the heating is an "indirect" circuit.
(Having a hot water cylinder doesn't necessarily mean it's gravity - it could be fully-pumped with a three-port valve. If it is, the valve being stuck is another suspect, since it carries out a switching function when it moves).
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I haven't got any three way valves there is a pair of 2 port valves. Both in the auto position.
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...the function of these is the equivalent of a three-port valve, but I'm not familiar with the wiring. I strongly suspect that the switching function is similar to a three-port, though.
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Yes it would make sense to perform the same function but a different set up.
I moved the lever valve on one, i could feel resistance and it sprung back to auto when released.
The other doesn't feel connected to anything and moved freely with no resistant.
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...just had a quick look at a 2 x 2 port S-plan wiring, and certainly if the CH diverter is stuck in the wrong position, then the pump switching won't work (and the boiler won't fire).
The suspect seems to be the valve that is buzzing (conventionally they seem to be "motor open" which means if the motor fails, the appropriate circuit will be closed and switching will be "off").
This seems a decent description and saves me typing:
www.heatsy.co.uk/blog/zone-valve-aka-2-port-valve/
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From that link,
If the external controls are calling for heat and the lever on the zone valve moves freely but the boiler doesn’t come on, it’s likely the motor has failed, or you have another electrical problem.
That's what is happening.
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The motors fail because they are driven all the time, to the point they stall, when heat is required
You can strip the valves and replace the motors, done it loads of times, or even buy a complete new motor/switch assembly. Its called the "valve head'
Last edited by: Zero on Fri 18 Nov 22 at 16:48
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You can strip the valves and replace the motors, done it loads of times, or
>> even buy a complete new motor/switch assembly. Its called the "valve head'
>>
www.toolstation.com/honeywell-home-v4043v4044v4073-valve-motor/p99980
You mean change this?
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... and that was the same for me, albeit 3 port. I read you can change the electrical bit on the top cos it may just be that, but it's still a few bob and my plumber said to change the lot anyway while you're at it
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>> ... and that was the same for me, albeit 3 port. I read you can
>> change the electrical bit on the top cos it may just be that, but it's
>> still a few bob and my plumber said to change the lot anyway while you're
>> at it
But by changing the head, you dont need to drain down. They are usually all the same,
www.amazon.co.uk/Motorised-Diverter-Replace-Honeywell-V4043C/dp/B00WBIYYG0
Last edited by: Zero on Fri 18 Nov 22 at 16:52
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True, but my man drained it just enough to be able to take the pump off, not completely.
If it's an older system I'd def be looking at doing something about any sludge build up.
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Had my three way valve replaced last week for similar symptoms. You can often wiggle the slider to change the valve position, or a sharp clonk with a hammer can dislodge some carp, either of which may be a temporary fix.
But it'll likely stick again. Had mine replaced with a half decent one - £120ish plus fitting. it took not much more than an hour to do.
AIUI The boiler generates hot water which is shifted round by the pump but if the hot water never goes anywhere because the 3 way valve is stuck on water then the pump will not know to fire up.
I was planning on power flushing my system soon and this just reinforced the idea, as I'd when they changed my cylinder in the summer they identified sludge. I put some sludge buster in the system which can be there for up to four weeks, then will flush it in early Dec.
But I'm no expert.
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>I was planning on power flushing my system soon..
I've read conflicting reports about 'Power Flushing' an old system. The only certainty seems to be that it's a nice little earner for plumbers. ~£800 for half to one day watching a machine.
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>>Power flush... £800
Yes that's the sort of price I have seen.
We had it done whilst they were doing other work so not so costly as it took an hour or so to set up the machine, then they got on with other stuff.
I did wonder if I could have sourced the chemicals more cheaply but then I wouldn't have known how to actually use them though.
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>> I did wonder if I could have sourced the chemicals more cheaply but then I
>> wouldn't have known how to actually use them though.
There's no point in adding chemicals that just dissolve the sludge, you need to flush it out down the drain (don't tell the tofu munching, eco warriors). The place I bought earlier this year had a flush machine running most of the day - you should have seen the black sludge that got flushed!
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>>black sludge...
Yes. Saw it come out the other side of the pump. Horrid stuff.
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>> I've read conflicting reports about 'Power Flushing' an old system. The only certainty seems to
>> be that it's a nice little earner for plumbers. ~£800 for half to one day
>> watching a machine.
Its a pre requisite for the guarantee on a new boiler. And most of them now insist on a magnetic filter in the system as well.
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I've read conflicting reports about 'Power Flushing' an old system. The only certainty seems to
>> be that it's a nice little earner for plumbers. ~£800 for half to one day
>> watching a machine.
>>
>
I think our neighbours had this done once. Looks a bit like a washing machine that pumps out a load of sludge?
I wonder who much the machines are?
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HSS hire them out with full instructions for under £100 for a weekend, plus you need to buy some additives.
www.hss.com/hire/p/central-heating-flusher
and the instructions are here www.hss.com/medias/sys_master/docs/docs/8961586495518.pdf
I'm doing it early in Dec.
Luckily I have a plumber next door who will help me with setup and breakdown if need be - I think I'll be OK with that really as it can go in where the (newish) pump is, which has isolators each side, so the only other messy bit could be draining the system. Undoubtedly the system will need bleeding etc after the event.
I watched it being done years ago and it really is a simple job which just takes time. Essentially you turn off all the rads and flush is one way then the other till it runs clean, then turn on rads one at a time and do the same.
EDIT: If you are thinking of doing it I'm advised that it's worth putting the stuff in the break down the sludge a good 3 - 4 weeks before. That's easy, I just held the float down in the expansion tank, drained a bit off the system and added the pot of stuff to the tank. I drained some just cost I thought that would more likely send it into the system than if I just poured it into the tank, when it might never go far.
Last edited by: smokie on Sat 19 Nov 22 at 10:12
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An explanation and wiring diagram of S-Plan (2 x 2-port) boiler controls.
flameport.com/electric/central_heating/heating_wiring_S_plan.cs4
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The diverter valve(s) are commanded to work by the thermostats/programer, they move, make a microswitch to command the boiler, the boiler commands the pump (because it needs to run the pump after the heating cycle to prevent heat soak in the heat exchanger)
If you have have an open vented system boiler, which it sounds like. Sounds like you valve(s) are borked, they fail the most in any system
Last edited by: Zero on Fri 18 Nov 22 at 16:40
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It does look like it.
This looks the closest to what is fitted now.
www.toolstation.com/honeywell-home-powerhead-for-v4043h-valves/p19864
I'm guessing the brass valve can be left and just swap the actuator.
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...big advantage about toolstation/screwfix is, if it is urgent, you can generally pick up immediately.
OTOH, such items are invariably rather cheaper on eBay (where plumbers and plumbing suppliers are selling off bulk purchases).
It always pays to be wary of quality, but this is an example:
www.ebay.co.uk/itm/401745048475?hash=item5d89def39b
The manual lever, if functioning, may well have a latch on the other end of the travel from "auto". If it has, latching it there should open the valve and complete the switching. (even holding it there should enable testing). I wouldn't leave it latched for a long time (though if you have a thermostat in circuit it would probably ultimately be OK) but it may provide a diagnosis with CH selected.
Last edited by: tyrednemotional on Fri 18 Nov 22 at 17:28
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Before you go changing valve heads Sooty, have you checked that the room stat is actually switching?
If it is, looking at the S-Plan wiring diagram there's an easy way to check each circuit.
For the radiators, switch off HW at the timer then take the cover off the 'heating' valve and turn the room stat to maximum (it helps to have an assistant). You should see the valve motor run to open the valve. If the motor doesn't run either the motor is duff/jammed, it's not getting power from the room stat or it's neutral is open circuit.
If the motor runs but the pump and boiler don't fire up, it's the microswitch or wiring to the boiler.
If you're comfortable with electrics a neon screwdriver is all you need to check for power. The signal from the valve microswitch to the boiler should be the Orange wire.
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>> Before you go changing valve heads Sooty, have you checked that the room stat is
>> actually switching?
>>
Too late, I've swapped the valve motor. The boiler now switches on when demanded through the hw/ch control.
Rads upstairs are hot pretty quickly. Downstairs are a bit patchy though, most fine. But two aren't really getting upto temp.
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From my limited understanding a central heating failure could be the result of any one of a number of things misbehaving. If the HW is working, it seems likely the boiler is functioning properly.
The room thermostat (I assume just one) needs to send a signal to the boiler that the temperature is below that set to enable the boiler to fire up.
The boiler may have a water temperature sensor for the central heating circuits in addition to the hot water on a separate circuit.
There will be a valve in the system which allows the HW to operate independently of the CH. These can seize which you may be able to free off or lubricate.
The pump may have failed - the hot water may still be OK if the tank is gravity fed.
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There was mention above that one valve had no resistance which would suggest it is stuck in the open position.
The micro switches also fail.
Nothing much to loose changing the complete motorised unit.
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Son had a similar issue 6 months ago. HW but no heat in radiators.
It was the small cold water tank being empty - the float had stuck - filled with water and all was well.
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Thanks to all for the help. The boiler now works on the CH side.
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It's clearly the time of year for stuff to die. My CH pump decided to move on from this world yesterday.
Replaced faulty component (capacitor) and re-installed after trip to Screwfix for new seals.
Now the gate valves leak. Back to Screwfix.
New gate valves installed. All seems good until I return to the boiler 20 minutes later to discover it swimming in an inch of grotty water.
Eventually track the leak down to one of the air vents on the top. Grant-specific, not in stock anywhere easily accessible and of course the installer stole the emergency sealing caps when he fitted it in 2009.
With some significant abuse from molgrips and Stilsons I managed to get the air vent off with the intention of sticking a temporary cap on. But no, despite being made by an Italian company it's a 5/8" fitting.
At this point I resorted to flushing it out in the sink with a fairly toxic cleaner and boiling water. A load of debris came out of the air vent and so far (touch wood etc) it's back together and not dribbling water.
House seems warmer too since I get the distinct impression that this is the first time the heating loop has been changed since it was built. Knocked the pump speed down to 2 and it's working pretty much as the manual suggests with a 20-25C temperature split between flow and return.
The water that drained out was the same colour and consistency of the oil that comes out of an old diesel engine.
I can also advise against bothering to purchase "Home Emergency" cover from your insurance company. It wasn't very much but it turns out that they have exactly one guy in the whole country who does oil boilers, and tentatively booked me in for Wednesday.
Always important to be reminded how much I hate plumbing. At least oil boilers are simple if you pull the burner out.
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"Always important to be reminded how much I hate plumbing."
I'm the same. In the last year I can't even count the stuff I've had done, much seems due to me changing the boiler when I didn't need to 2 - 3 years ago.
Since spring I had the pump, 3 way valve, and water cylinder replaced. In the last two weeks I've had a sewer blockage, which pretty much knocked out both loos and took well over a week to get resolved.
Today SWMBO noticed an overflow dripping fairly fast. Turns out it's the cold tank in the loft, full to the overflow. I can't readily see how to adjust the ballcock as it seems to be slid down the bar as far as it can be already (any ideas??) and I don't get why it's just started. When I looked at it, I was reminded that that tank and gubbins was only replaced a year or so back. At least if anything needs replacing it won't be too costly!!
EDIT: since found that bending the arm is the trick. Just need to make sure I do it the right way!! :-)
Last edited by: smokie on Sun 20 Nov 22 at 11:31
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If it wasn't leaking before but it is now, then chances are the washer has failed or there is a bit of grit stuck in; unlikely it just needs adjusting....
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Yes, that's true. I'm going to be keeping an eye anyway, it's easy enough to spot as it overflows onto the garage roof.
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>> Son had a similar issue 6 months ago. HW but no heat in radiators.
>>>> It was the small cold water tank being empty - the float had stuck - filled with water and all was well.
>>
Autumn a few years ago , time to start using the CH and I too had no heat in the radiators.
Called in a plumber and... sucks teeth....I can see it is an old system etc. They do not last for ever. Suggest new properly insulated HW cylinder and a new boiler. The fact that " I have a few brochures in my car....
Thought some more about it. Inspected the header tank, waggled the ball valve and the tank refilled and all was well.
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When the (galvanised) cold water tank in my loft started leaking due to rust I replaced it with a plastic one. I put an isolating valve in the water supply. That failed several years later and started leaking from the screw.
I've now a de-humidifier and wrist support as a result of removing the sodden loft insulation! At least the ceiling didn't come down.
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Hot water pump CH - Terry
