I have quite a large house with a single storey extension on the back. It is a gravity fed oil fired central heating system with an adequate boiler size for the house and the CH pump is a Grundfos UPS 15-60. However since we have been in the house built from new the radiators in the extension are at best warm whilst the rest of the house heating system seems fine. I have balanced and cleaned the system as much as I can but these radiators in the coldest part of the house never really get warm unless I turn the majority of the other rads off. Also the boiler has to be set at virtually at its max to prevent the internal thermostat turning itself off without adequately warming any of the radiators throughout the house. The boiler then cuts in and out frequently but is obviously an inefficient way of operating the boiler until eventually the house thermostats come into play. It all sounds like a circulation problem to me and probably caused by poor design. However it is too late to rectify the design and replacing all the CH pipes as the cost, chaos and probably a divorce to boot so this is not an option. This leads me to my question, I am considering changing for a larger circulation pump to increase the flow and/or pressure around the system. Before I go through the significant purchase cost of such a pump I would like expert opinion on whether I am on the right track or doing this a waste of time and may not provide the solution to the cool radiators and inadequate circulation through the boiler?
a larger pump should help. there are no garrantees tho. sounds like the pipework to the extension is badly under sized and maybe the system could have alot of corrosion. When you drain the system down take a downstairs rad off, tip it towards a bucket, if its sludgy the system needs flushing.
Hopefully not down to corrosion as the problem existed from new. He's also tried balancing the system and finds that the extension does heat up but only when the other rads are partially shut down. It certainly does sound like either an underpowered pump or poor design as Itchy says. Very stupid Q - the pump is on III - high speed?! Could an alternative to replacing the pump be to add a further one, somewhere on the return leg of the system but positioned not to allow the risk of drawing in air into the system from the vent pipe? They'd simply be joined in parallel, and possibly both be able to be knocked back a speed to I or II. The system would then need balancing again or the main house rads will simply get too much flow - noisy. If the extension is fed by a noticeably long flow pipe, could a second pump even be fitted on that section, and set to low speed? Or am I talking bar locks... OP, you say it was like this from 'new'; do you mean new house or new extension? As Itchy says, you should of course also check for sludge, but hopefully that ain't the cause as you say it was like that from new.
the cental heating 'pump' is badly named it's not a pump but a circulator, A pump is something that forces water or air from one place to another, think of it like a bike chain one side's push'n the other pullin' and as long as the links are all connected it does't really matter how long it is, in the pipes there's no links but water, and air in the water can cause gaps ( broken links) this is a more likely cause, course I'm just a ****** plumber but that's where I start lookin,
Was the extension added after the boiler and pump were installed? How do you know the boiler is an "adequate" size for the house? Which boiler do you have? What proceedure do you use when balancing the system? There's no point changing the pump if you don't know why the rads don't heat up.
Thanks for all your replies it is much appreciated. Okay, some more information. The boiler is a Grant 90/120 which according to the spec provides a max of 120,000 BTu. I have done a rough calculation on the demand for the radiators and it comes to about 100,000 BTu which doesn't give too much flexibility but does adequately heat the house except for these radiators as described above. The extension was built at the same time as the house and the "plumber" who installed them did so as part of the initial installation and they have always performed the same. Regarding balancing, there is a radiator downstairs in the hall with no TRV which I had to wind down the lockshield so that it improved the flow to the others and is now the last to warm up (except for the extension ones). Upstairs - regarding the non TRV radiators there is one on the landing and a towel rail again these have been wound down until they are the last to heat plus the other bedroom radiators are closed down to ensure all the hot water does just chase round the upstairs. The house has 2 thermostat and zoned by the programmer for upstairs and downstairs.
120,000 is the input: the output is 110,000 or 32.2kW in current terminology. So you added up the outputs of the rads, assuming they had been correctly sized? It's better to work out the heating requrement of the house using the Whole House calculator at http://www.idhee.org.uk/calculator.html From your description, the system has never been balanced properly. Try this: Remove all TRV heads and set the wheel valves on other rads to full open Close all lockshield valves (turn clockwise, looking down) then open one-third of a turn Set programmer so both zones are heating up and set stats high so boiler runs Let system get up to temperature The aim now is to get all returns at approximately the same temperature Check (by feeling) the return (colder) pipe of each rad. Choose one which is in the middle of the range and use it as a benchmark Close down the LS valve of hotter rads by 1/12 turn or less. Check all rads again Repeat until all returns feel about the same and there is a noticeable difference between flow and return. Replace TRV heads and wheel valves; set as required. Set thermostats as required. If the stats turn off the boiler before the rooms are up to temperature, close the wheel valve, a bit at a time, until the problem goes away. Do you have a bypass on the system? If so, what type?
Hi Sam, Thanks for this. Its sounds like a job for this Monday when the forecast says rain all day. Just want to confirm, do you mean 1/12th ie 30 deg turn increments on the LS. My only query is that some of the valves in the main part of house are virtually closed to get heat to the others? The second question is a sign of my ignorance as I am not sure whether I have a by pass or not on the system, can you guide me to where and what I should look for? Cheers Barrie
If you have a bypass fitted it will be after the pump but before the zone valves, it will either be an automatic valve, but probably from your description a manual valve which will link the flow and return with probably a gate valve either with or without the red handle. Do you have a Y plan system or S plan. As you won't need a bypass with the Y plan and can close it off fully if it's fitted. One thought, what size pipe work do you have coming off the boiler and to the pump, if it's 22mm it may be too small to cope with the new extension, you may have to upgrade to 28mm.
If the system has never worked a 100% from installation did you ever call the plumbers back in so they could rectify the problem.
Yes. Smaller is even better. I forgot to say that you should allow 10 minutes for the system to settle down between changes. Altering one rad will have a knock-on effect, so you need to check regularly. Compared to the flow through the main pipes, the flow through each rad is small, so the LS valves do not have to be open very much. PS Don't expect perfection.
The OP says he has stats upstairs and downstairs, so presumably two zones, which implies S Plan. That's why I asked about a bypass.
you DO need a by pass on a Y plan too, if the system has TRV s and the hot water's satisfied then the system can hydoblock and it'll damage the circulator/pump
First of all no we didn't get the plumber back as we bought the house in summer and so we didn't know anything wrong for several months and other things were going on at the time. And yes we should have but we are where we are and we are paying the price for it now in trying to get these radiators to operate at a higher temperature. The system is an "S" plan plus, from what I gather from the inf from the net and there is a manual valve on a 15 mm pipe from just past the pump and links to the bottom pipe feeding the hot water cylinder heating coil. This valve is fully open at the moment? The pipe is 28mm and appears to go all the way to the boiler on the main feed and return circuit. Just after each of the two port valves for the individual heating zone these drop down to initially 22mm but obviously I cant see where they drop down again to feed the radiators downstairs with 15mm.
You should be able to get the building company back out to sort out any snagging with a new build,in less they are no longer trading. I have known snagging work to go on for a few yrs with new builds and it sounds to me that the heating was never commissioned properly in the first place,the end of the day you wouldn't buy a new car with heaters that don't work and try and sort the problem yourself,so why do it with a house that has cost you far more money. All I'm saying is don't just sit back and take it.
Hi Plumberboy, This is one that I know what I should have of done and I am now on a bit of a guilt trip for not doing so but for several reasons I didn't. Now it has been several years and beyond what the builder if I could find him or even they are still in business as it was one and his dog operation would be prepared to cover at their cost. As far as I can see I have a couple of options (a) suck it up and carry on living with the issue as we have done for the previous years (b) try whatever comes out of this string (c) buy a new pump and hope it cures it at the associated expense but there are no guarantees or (d) get a heating engineer in and see what they say. I will obviously have a go at balancing the system again as this is the cheapest option. Thanks again for the advice it is appreciated and if nothing else I know more about my CH system now than I did before.
Your correct about the S Plan plus. If the valve on the 15mm pipe is fully open, no wonder you are having problems. A lot of the water will be flowing straight back to the boiler instead of going through the radiators. The manual valve should really be replaced with an Automatic Bypass valve. This really needs to be done before trying to balance the system.
Thanks. I presume the automatic valve senses if there is increased pressure due to all the TRVs reaching temperature and shutting off all the recirc flow and hence bad news for pump. But why did the plumber put a manual one on? To try and see if this cures the problem could I turn the valve into the off position. As I say there are a couple of radiators that have no TRVs which I thought would protect the pump at least in the short term?
It's no so much bad news for the pump as noise in the system when the pressure increases. Also, TRVs do work so well if the pressure across them is too high. Auto bypass valves are fairly new; it was standard practice to fit a manual valve and adjust it as best as you can. I wouldn't close the valve completely; set it to one turn open and see what effect it has. As your boiler does not have pump overrun, there would be no harm in trying this out.
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