Boiler troubles

[Nigel Watts]

Having had a heating engineer in to fix it in January the problem has come back.

Boiler fires up when it should but goes off after about 30 seconds. A few minutes later it does the same, ad infinitum. Result: water in tank and radiators is tepid at best.

I think it must be a fault in the water circulation system between the boiler (ground floor) and hot water tanks (we have 2 on the 1st floor). There is a pump next to the boiler which seems to come on as it hums and vibrates. There are three electrically operated valves on the first floor on the pipe coming up from the boiler, one on the input to the coil on each tank and the third at the start of the central heating loop. All three appear to be free and working. I experimented with opening the tank valves using the manual override but it did not solve the problem . The system is fully pressurised and does not seem to have air in it.

The engineer is coming back tomorrow, so I would like to know what to ask him. My guess is that the problem lies either with the pump near the boiler or inside the boiler, e.g. a faulty thermostat, by I am no plumber. Any ideas?

 

[Sonyaclegg]

Could be a pressure problem. It won't work if the pressure is too low. I had a similar problem and found a solution on YouTube which was very handy. I worked my way through the boiler instruction manual to no avail then turned to YouTube as a last resort! There are lots of clips regarding boiler faults that may be of some assistance to you. At least it may help until your engineer returns.

Hope you are warmer soon.

 

[MdB]

Pump stuck? If this is the case, it will get hum and get hot.

I believe this is a common problem and happened to us. Option 1, hit the pump with a rubber hammer, bit of wood etc. Option 2, remove cap from centre of pump (penny or big screwdriver) turn pump manually with a big screwdriver - expect some water leakage. Option 3, leave it to the plumber.

 

[Owain]

Another vote for stuck pump.

If it's not stuck pump you might have an air lock.

It's quite handy if there are gate valves each side of the pump allowing it to be removed easily.

 

[Nigel Watts]

Engineer came and replaced pump. We'll see if this fixes it.

 

[worms]

Boiler fires up when it should but goes off after about 30 seconds. A few minutes later it does the same, ad infinitum. Result: water in tank and radiators is tepid at best.

Are you on oil or gas?

If oil, it could be related to the boiler ignition sequence. On mine the fuel/air mix alters at 30 seconds after initial lighting and settles into its normal running mode. If the air supply isn't right and it is running too rich it then shuts down. On mine it goes to lock-out but I guess some systems might allow repeated attempts at ignition. I can also experience issues if the photo-cell doesn't recognise that the flame is lit and again this can lead to it shutting down at that same 30 second switching stage.

My experience of circulation pump airlocks is that the boiler runs normally until it overheats and goes to lock-out, at which point the pump is very hot and the input pipe cold (output pipe still hot due to heat from the hot water cylinder).

Hope your new pump has solved the problem!

 

[88v8]

If the pump stuck, the question is why?

Do you ever have to bleed the rads? If so, does the 'air' smell pongy?

Ivor

 

[Nigel Watts]

The system seems to be working OK now, but I am still working on balancing all the radiators.

The engineer said that the water in the circuit was a bit sludgy and may need to be flushed out and cleaned. He told me to keep an eye on the reading on the digital pump and if I see it falling (it currently reads 45) I should call and arrange the clean.

In the meatime I think I have finally diagnosed and possibly solved the problem of banging pipes in my bedroom radiators, which has been with us for years. Because the valves are thermostatic with a frost setting they can never be turned fully off, so banging could occur on any setting, even the minimum position.

These radiators are of unusual design, being very squat and having their input and ouput pipes right next to each other and going into the same casting so that you cant tell by looking at them which pipe relates to which valve. By feeling how the pipes warm up I have discovered that the pipes were fitted the wrong way round meaning that the thermostatic valves are on the outputs not the inputs. When I found out where they were (which wasn't obvious) I also discovered that the lockshield valves were fully open despite the radiators being relatively close to the pump on the circuit. I have now closed down the lockshields to restrict the flow. So far there has been no banging. If this fails, I believe one can now get bi-directional thermostatic valves which dont suffer from the same problem.

The more one learns about the different trades the less faith one has in experts' ability to get things right.

 

[MdB]

I thought all valves on radiators are bi directional and it doesn't matter if valve is on input or output?

 

[Owain]

For ordinary valves it doesn't matter.

TRVs are directional, unless stated as bidirectional.

 

[88v8]

If there is sludge in the system then the water treatment is inadequate - not enough, or diluted by leaks or alterations to the system with no subsequent topup. This will cause system corrosion and repeat problems with the pump.

Ivor

 

[Nigel Watts]

If there is sludge in the system then the water treatment is inadequate - not enough, or diluted by leaks or alterations to the system with no subsequent topup. This will cause system corrosion and repeat problems with the pump.

Interesting you should say that. The intermittent fault has returned in spite of my new pump, so sludge removal is next on my list.

I have just had a rather frustrating phone call with British Gas trying to arrange for the system to be drained and cleaned out. It seems I have to take two days off for this: one for someone to turn up to tell me what it will cost and a second to have the work done. Valuing my holdiay time as I do, I put to them a proposal that I would accept their quotation, however outrageous, so long it only required only one visit. This was not possible.

When they drain the system it will at least provide an opportunity to replace the valves on my banging radiators.

 

[PeterI]

The intermittent fault has returned in spite of my new pump, so sludge removal is next on my list.

I have just had a rather frustrating phone call with British Gas trying to arrange for the system to be drained and cleaned out. It seems I have to take

I used a guy called Joe Kenny (020 8861 6108 according to the Gas Safe website) when I lived in NW1. He has an office on St Pancras way so he might be more than willing to come round for a quick quote.

 

[masochists-r-us]

It appears that your boiler is heating up then shutting down because the heat is not being taken away by the rest of the system.
Heat is taken away via the water passing through the boiler, propelled by the circulation pump.
Therefore looks like a circulation problem.
I guess this could be the pump itself - which you have already replaced and so should be able to rule out. But some systems have two pumps, one inside the boiler and another to boost the flow. If your system is large then this may be the case?
However, you seem to have resolved problem, then the problem returns. Since you have not changed any of the hardware (pump excluded) this points to a blockage, possibly sludge.
Problem is where? It is likely that the blockage is in your boiler (as I am assuming problem persists on both domestic hot water and central heating - these are different circuits and so if problem occurs on both then the problem must be associated with the boiler).
If this is the case I am guessing boiler at least requires draining and flushing to return to working order.
You could flush the whole system when this is done. But you could also try installing a filter/dosing device (e.g. Fernox TF1) in the line to clean your system over time.
Having said all this could also be a faulty boiler thermostat.
I am on the verge of buying and installing a TF1 so if you go this route let me know how you get on?

 

[Baron de Gynes]

I've got a TF1 fitted in the system here and *touch wood* haven't had any problems with sludging yet. The filter has been cleaned out a few times and it appears to be doing its job.

 

[Nigel Watts]

But you could also try installing a filter/dosing device (e.g. Fernox TF1) in the line to clean your system over time.

About 18 months ago I had a gadget fitted to a pipe on the central heating loop which, I was told, would remove gunge and would be emptied each time the system was serviced. My last service was in January this year, yet when the engineer came to replace the pump earlier this week he remarked on how dirty the water was.

But some systems have two pumps, one inside the boiler and another to boost the flow

My system has four pumps. One next to the boiler on the ground floor which has just been replaced, one at the start of the central heating loop on the first floor next to the hot water cylinders (I have two), one in the basement at the start of the underfloor heating circuit and one in my ground floor side corridor to feed another underfloor heating circuit. The only pump which works the loop between the boiler and the heat exchangers inside the hot water cylinders is the one next to the boiler. When the boiler shut-down problem occurs the hot water does not get warm, so the other three pumps are unlikely to be the cause, whether they are working properly or not.

I have been wondering for a while if all my underfloor heating is working properly, or whether it was just under-specified. My side corridor for example is always cold in winter even though it has underfloor heating. It was built about 10 years ago The roof is double glazed as are the two external doors, but because one has warped badly they are not very draft proof. One of the basement rooms served by underfloor heating (which has two external walls) is also pretty cold. Their pumps however hum away and there is clearly some heat coming through. If sludge is the problem, and if sludge damages pumps, I am guess it could be worthwhile having the other three pumps checked out, especially the ones on the underfloor circuits.

 

[88v8]

If the system has a suitable concentration of water treatment it will never develop sludge. No filter should be needed.

Problems arise when there are leaks, or alterations, and the treatment is not topped up. The chemical is expensive, and bodgers/cowboys will not bother, knowing that they'll be long gone when problems arise.

Another source of problems is known as 'pumping over' and arises when the pump - or any pump in your case - is wrongly positioned in the system so that the pressure it develops results in water being pumped through the vent loop and falling back into the header tank. This aerates the water, and the constant ingress of fresh oxygen causes corrosion, which leads to sludge. The sludge is an iron oxide resulting from the inside of your rads corroding away. Pumping-over may only occur when certain valves have closed and the pump is working against back-pressure. I would say that in a complex system such as yours there might be scope for this, unless alterations have been made with a full understanding of the system design and dynamics.

The way to detect this fault is to go into the attic, find the header tank, and hang a plastic mug under the open end of the vent pipe where it returns to the tank. Go back next day, and if the mug has wtaer in, then pumping-over is occurring, and either the pump must be relocated or the feed and vent pipes repositioned relative to the pump.

Draining alone will not remove the sludge. Waste of time. This requires a full system flush under pressure, refill then repeat until clean. If there are no drain valves at the bottom of the system then it may have to be partly dismantled. I would not be surprised if it took two men a whole day.

After the process is complete it is essential that sufficient water treatment is put in. To do this the total system water content must be calculated - all the rads, boiler, hw loop, pipes (the pipes hold a lot of water) and header tank - so as to know the quantity of treatment required to achieve the necessary percentage.
The treatment chemical must be suitable for the boiler, if in doubt call the manufacturer. Generally, something such as Sentinel 100, or Fernox would be OK.
http://www.fernox.com/problem+solving/how+to+sheets/preventing+corrosion

Finally, the boiler must not be fired until the treatment has been put in - this would result in a flash of scale being deposited on the heat exchanger. Older boilers with iron exchangers were tolerant of scale, modern boilers with alloy exchangers are not, and will evince their distress by making banging noises when hot.

Ivor

 

[Feltwell]

That's good to know Ivor. I moved my header tank from being mounted on a wall in an attic bedroom ( :roll: ) up into the roof void. I noticed at the time that when the pump cut out, a splash of water would come up the vent pipe and into the header tank. The vent pipe didn't loop up very far above the tank - when I repositioned the tank in it's new, higher position I also made the loop above it much higher than before, which seemed to stop the problem. As it's in the roof space I won't see it now though, paranoia may just lead me to using your plastic cup trick!

I've a fairly large system and always chuck two bottles of Fernox in it if I have to drain it. I presume that - within reason - you can't overdose the system with that stuff? The plumber who replaced my boiler when we first moved here recommended using two.

 

[Feltwell]

Oops - just read your link after posting that

Over-dosing with anodic inhibitors is unlikely to have any detrimental effect.

So the motto is, if in doubt and it's a larger system chuck 2 bottles in. A bit more cost but much cheaper than repairs!

 

[Nigel Watts]

Ivor

Thank you for such an informative post.

My system is about 10 years old and has not been altered, nor does it have any tanks in the attic, being fully pressurised. What has happened over the 10 year period however is the taking off of radiators for decorating and subsequent replacement. Clearly when this happens water is lost and has to be topped uo.

I have a service contract with British Gas but this does not cover flushing out the system. The engineer I spoke to did mention flushing out. Someone is coming round in a couple of weeks to give me a quote and I will quiz them about it.