We seem to have something not quite right with our heating/hot water system. It’s a relatively simple set up - a system boiler, an unvented (mains pressure) hot water system and a vented heating system (header tank in the loft). The boiler works, the radiators get hot and the water also get hot. But, the radiators take forever to get warm, and in fact most of them never get piping hot all over. And, as I found yesterday after using lots of hot water, it takes literally most of the day to reheat the tank, when I’m sure it used to reheat it in under an hour.
As with many things in life, I know just enough to know I don’t know enough about heating/hot water systems to actually fix it, so I’ll be calling in a plumber. But, I do like to have a basic understanding so that I can have a sensible conversation with him/her.
My thoughts are:
Radiators taking a long time to heat up implies a circulation problem of some kind, and as they’re all affected, maybe the pump?
Hot water taking a long time to re-heat is likely to be related; if the boiler prioritises heating (does it? I’ve no idea) then if the thermostat keeps calling for heat the water will not get warm.
My other thought is that perhaps the three way valve that switches from hot water to heating is jammed? I am thinking along the right lines do you think?
Thanks!
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I'd start with a radiator bleed. Check water is flowing from the rads. There may be an airlock or even a blockage somewhere. A good summer saw hot water systems unused for an extended period.
Check the pump. You can feel it running with your hand.
The three way valve as you suggest could be stuck. There should be an overide on the motor allowing you to manually open. Give that a try with the system running. You should feel the pipes get hot if the water starts running through them.
Do you have a copper tank. If so there may be an exterior thermostat on it. This could have been knocked and wound down cooling off your hot water. Your boiler may also have a thermostat on it and likewise may need tweaking up.
Last edited by: Fullchat on Sun 25 Nov 18 at 13:38
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My first move would be to vent any air from all the radiators, particularly if they only get hot, or warm, at the bottom.
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Due to the long heat up time for hot water, my thought are airlock or pump. Don't think it's valves as the boiler wouldn't fire up unless they operate the microswitch. Always a good idea to bleed rads once a year
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Thanks both - yes, bleeding the radiators was my first port of call, though as they were hot at the top and just warm at the bottom I didn’t think there was air in the system, or at least that wasn’t the issue. I hadn’t considered an airlock/blockage at the beginning of the pipework though, so thanks. I was working on the basis that as all radiators seemed to be similarly affected it was a pump issue. I’ll invstigate the three way valve as well, thanks. Though, while I know of its existence as part of the system from a theory perpsective, I don’t actually know where it is ;) Time to go looking!
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I;d also look at balancing them properly. I did it once and it made a surprisingly enormous difference. Quite easy to d-i-y, and it's on my agenda for this winter. See here for how. www.homebuilding.co.uk/how-to-balance-radiators/
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>>bleeding the radiators was my first port of call, though as they were hot at the top and just warm at the bottom
That could also indicate sludge in the system. My in-laws had that problem, one summer I removed the rads and flushed them through. The amount of muck that came out was remarkable.
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Thanks... I did briefly consider sludge, but discounted it on the basis all the radiators were replaced 6 or so years ago, and all seem to be similarly affected. But worth investigating I think.
On No FM2Rs question, the boiler is gas. I hadn’t considered that it wasn’t working properly, as it fires up just fine, doesn’t make and odd noises and is not showing any error codes on its screen. But the question did make me watch it more closely...
The water temperature on the boiler is set at 72 degrees C. I assume that’s the temperature it aims to get the water passing through it to. It manages that just fine, and then ‘throttles’ back to 2 or 3 (out of 5) flames on its equivalent of a rev counter for a while. Then stops. Repeats the cycle a few minutes later. So it looks to me as if the system as a whole can’t get rid of the heat generated by the boiler quickly enough. Otherwise the boiler would stay on for longer, given that the thermostat hasn’t reached its set temperature wouldn’t it? In my mind that makes it more likely to be a circulation problem, either airlock, pump or blockage?
Edited to add, I found the three way valve easily enough. It’s a grey thing with Drayton on it. Whether it’s relevantbor not I don’t know, but the pipe into it and both pipes out seemed to be the same temperature to me, that is to say just a bit too hot to hold!
Last edited by: PeterS on Sun 25 Nov 18 at 16:58
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>>can’t get rid of the heat generated by the boiler quickly enough
Indeed. And that would be anything related to flow. Bit if it allows it's temperature to drop below 72 then I wonder why?
Or perhaps the thermostat / Heat sensor is overreacting and cutting power too quickly so the water is not being sufficiently heated.
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>> Indeed. And that would be anything related to flow. Bit if it allows it's temperature
>> to drop below 72 then I wonder why?
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>> Or perhaps the thermostat / Heat sensor is overreacting and cutting power too quickly so
>> the water is not being sufficiently heated.
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I’m assuming it lets the temperature drop below 72 because it can’t maintain that temperature while still burning. As soon as it goes above it it first throttles back and then cuts heat altogether. Once it drops to 50ish it fires back up again. The heat sensor is a good shout though. All food for thought. Will call the plumber tomorrow. Though he’s probably called a heating engineeer ;)
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>> The boiler works,
No, I suspect that it does not. Or at least not properly.
How is it powered?
The radiators get hot, and get hot all over, just not quickly and not extremely. So everything is working, just lacking heat.
The water gets hot, just not quickly. So everything is working, just lacking heat.
If it is electric, then I'm guessing partially failed heater element.
If it is gas, then I'd be wondering about the gas flow.
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I'd be inclined to look at the pump. Grundfos pumps have a silver screw cover about an inch diameter when removed let you engage a small straight scewdriver in the end of the motor armature to turn if said part is stuck, good luck.
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When was the boiler last serviced? Could it be getting enough air for the burner to run efficiently? Can you see the flame, does it look yellow, rather than blue?
I've an installation manual for my boiler that shows the height of different colours of the flame.
I had a boiler problem where the gauze air filter had become blocked resulting in incomplete combustion. Apparently it produces alarming quantities of carbon monoxide.
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Thanks everyone. I feel more informed, so hopefully conversations with the plumber will be constructive!
The boiler was serviced a few months ago btw, and has no visible flame so can’t confirm its colour. But it certainly seems to get up to temperature quickly enough, then throttles back. I don’t think heat is getting away quickly enough to allow it to keep burning.. whether that’s the pump, an airlock or sludge I don’t know. But my gut feeling is if it was sludge hot water wouldn’t be affected? But then again I don’t know how it chooses heat or hot water if both are called for at the same time!
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>> again I don’t know how it chooses heat or hot water if both are called
>> for at the same time!
With a three way valve, shortest flow path gets the most hot water, so that hot water.
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"The boiler was serviced a few months ago btw,"
........ so my money is on a duff circulatory pump.
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>But my gut feeling is if it was sludge hot water wouldn’t be affected? But then again I don’t
>know how it chooses heat or hot water if both are called for at the same time!
Sludge usually builds up where water flow is slowest which is the bottom center of radiators.
Your problem sounds very similar to one we had last year after having some rads relocated and replaced with vertical units.
Draining down the system had dragged some limescale out of the header tank and it had partially jammed the pump impellor. The heating guy put one hand on the pump and knew straight away what the problem was because the pump was humming but not turning and was much hotter than it should be. He backed off the big screw on the face of the pump, gave it a few whacks and tightened up again. There was a tinkle from the pump and you could hear water begin to circulate. He also mentioned that the hot water cylinder takes around 80% of the boiler heat output until cylinder is up to temp.
To do a basic check of the 3-way valve, stop and start demand for hot water and watch the valve to see/hear if it moves.
Be wary if your heating engineer says that the system needs a power-flush. The guy who installed our new rads said that it's a good money-spinner but is only usually necessary when installing a new boiler because some boiler manufacturers demand it to satisfy their guarantees. It can also cause leaks in older pipework. Our guy drained and refilled our system with fresh water and some cleaning additive and came back a few weeks later to repeat with some protective stuff.
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>> Be wary if your heating engineer says that the system needs a power-flush. The guy
>> who installed our new rads said that it's a good money-spinner ...
Reminds me I had a Kamco (?) flush many years ago from BG. Took best part of a day and was effective at whatever it was we were trying to sort out. But it may have been a sledgehammer to crack a nut for all I know. And was quite costly.
Last edited by: smokie on Mon 26 Nov 18 at 00:40
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So what did the plumber say was wrong?
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>> So what did the plumber say was wrong?
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Well, he’s not coming until Tuesday next week; it’s that time of year I guess!! Will update when he’s been :)
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>>>Well, he's not coming until Tuesday next week; it's that time of year I guess!! Will update when he's been :)
Soooo?????
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>> >>>Well, he's not coming until Tuesday next week; it's that time of year I guess!!
>> Will update when he's been :)
>>
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>> Soooo?????
>>
Oops...sorry! Dodgy pump was the culprit. Whether blocked or actually faulty I don’t know, but it’s been replaced and normal service has been resumed :)
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yeah pumps just don't last for ever
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>> So what did the plumber say was wrong?
He sucked his teeth.........
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It's either the pump or the 3 way valve (although there is an outside possibility that a manual valve somewhere has failed in the part open position, but that seems unlikely). I've never seen inside a 3-way valve, so unsure if it fails in a partial position if it obstructs the flow. However, there should be a lever on the side which allows you to manually move the valve. If you put it to the heating side that would allow you to rule out (or in!) the valve.
My money is on the pump however....
Last edited by: RichardW on Thu 29 Nov 18 at 12:48
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>>My money is on the pump however....
I concur - pump full of black crap reducing its output.
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can you feel the pump vibrating, and is hot .or red hot
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is the pump on the highest of the 3 setting speeds . is the pump the correct one ,has the system been added to. try turning the flow valves tight on the nearest rads to pump side
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not sure if you already told us - do you have TRVs. They can easily seize up in summer in OFF position. Check that pins are free to move by removing the thermo bit of the body and checking the pin for free movement.
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do you have deep baths and keep topping it up, like i do. then yer your heating might go down a bit for a while
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Power flush is a money spinner and can often do more harm than good to an old system.
My central heating system has microbore pipes about 35 years old.Some of the valves have been replaced on the radiators.I have a thermostatic valve on one radiator.
I have never seen the point of these valves all our radiator valves are fully open.In the whole house to keep warm.The main thing with any boiler be it combi boiler or not have them regular serviced once a year.We live in a very hard water area so I add protection every year to the system.Combi boilers last about ten years after that is anybody's guess.
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Heating question - Fullchat
