Are you having trouble with a faulty regular boiler?

Being stuck without heating or hot water can be particularly tough, but whether it’s a serious problem or just little niggly faults that are easily fixed, I know from years of experience that having a faulty boiler is at best an inconvenience, at worst a stressful nightmare.

Having been a heating engineer servicing the Edinburgh area for over 20 years, I’ve personally dealt with more than my fair share of regular boilers, and know what makes them tick (or fail to tick, in some cases).

That’s why I’ve used my expertise to put together the top seven common regular boiler faults, and their fixes, so you can get an idea of the root of the problem, and how involved the work will be before calling in an engineer.

NOTE: Remember, DO NOT try to fix the problem yourself, unless it’s a very simple fix such as swapping a thermostat, topping up water pressure or defrosting a frozen condensate pipe – for everything else, always call a Gas Safe registered engineer.

About regular boilers

Regular boilers are often also referred to as ‘heat only units’. The reason for this is that it is essentially just a unit that heats, and has to be connected to radiators and a hot water cylinder – the motorised valves and pumps are all fitted separately, too.

You’ll have a feed and expansion tank fitted at a higher level than the boiler to fill the boiler, system and radiators with water. In recent years, regular boilers have improved dramatically and there are now highly efficient condensing models available that can be flued vertically through the roof or horizontally through the wall, with energy efficient controls.

Much like system boilers, a lot of faults with regular boilers may not be with the boiler itself, but with the external controls or the hot water cylinder. So, I’m going to note these faults first.

Fault 1: Boiler ‘kettling’ or making a banging noise

If your boiler is coming on for only around five minutes, and your boiler and pipework feel very hot but no actual heat is going to the radiators or hot water cylinder, it could be down to a faulty pump. Another big clue is if your boiler seems to ‘kettle’ and make a banging noise. Once it’s cooled back down, it may repeat the cycle again.

The Fix: The external pump is likely either sticking or burnt out, so get an engineer to replace it.

Fault 2: Upstairs radiators failing to heat

If your upstairs radiators are failing to heat, or you have to air/bleed them every day because they seem to be constantly collecting air, this is usually caused by a blocked cold feed or expansion pipe. Because it’s an open vented system, the water expands and contracts in these pipes.

If the system is particularly old or hasn’t been flushed in a few years, it may have sludge built-up inside. The water expands up, but takes time to drop back down through the sludge build-up, causing air to be drawn into the system.

The Fix: Have an engineer flush the system using a heavy duty central heating cleanser such as Sentinel X400 or X800 cleanser. The system should be thoroughly flushed, but it may also be necessary to cut out and replace the blocked pipework.

Pro tip: If regular boilers are drawing air or having circulation problems, sometimes the only solution is to pressurise the system. You can solve the problem by fitting a remote pressure vessel and making the expansion tank obsolete. The existing pipework should always be checked for leaks and integrity.

Fault 3: Expansion tank overflow leaking

If your boiler’s expansion tank overflow is dripping water to the outside, it could be a faulty ballcock that requires a washer replacement.

But first, check to see if the water is hot, as this could also be something more serious like the a split in the coil ofthe cylinder causing domestic water to push hot water back up to the expansion tank, which then overflows.

The Fix: It could be as simple as replacing the ballcock washer, however, if you have a faulty cylinder then it’s best to call in the experts and get the indirect hot water cylinder replaced.

Fault 4: Pump running constantly or boiler coming on by itself

Can you hear your boiler’s pump continually running? Or perhaps your boiler is switching on by itself for no good reason. This is usually a clear sign of a faulty auxiliary switch on one of the motorised valves. This causes a live feed continually to the boiler, which explains why it seems to be acting so oddly.

Sometimes this problem can be mistaken for a faulty time clock or thermostat, but on this occasion, replacing these will not solve the problem.

The Fix: Get an engineer to replace the faulty motorised valve.

Fault 5: No heating or no hot water

If only your hot water, or only your heating isn’t working (in other words, one or the other, never both at the same time), this is usually caused by a faulty 2-port or 3-port motorised valve.

The Fix: Get an engineer to replace the motorised valve head (if it’s a detachable, modern version). Alternatively, he/she could try draining the system and replacing the valve before refilling the system and adding inhibitor. Sometimes, it’s also possible to replace only the synchron motor on the valve.

Fault 6: Water far too hot

If you find your hot water is suddenly far too hot, it could be there’s a fault with the cylinder thermostat. Another tell-tale sign of this is if your central heating is working fine with no temperature issues.

The Fix: Because this is a regular boiler (not a system), it should be an easy straight swap to replace the cylinder thermostat if you currently have a standard vented (indirect) cylinder. However, if for some reason it looks a bit more complicated, or you are unsure, call in an expert.

Fault 7: Frozen condensate

If the temperature outside has recently dropped, with visible frost, whilst your boiler is acting up and your heating refuses to come on, you’ll most likely discover all the signs point to a frozen condensate (if it’s outside).

The Fix: First, find the condensate outside, and if you can, try using a kettle of hot water to thaw it out. Next, remove the condensate pipe below and drain to a bucket. That should fix the problem, but ask an engineer if he/she can retro-fit a condensate trace heater to stop this reoccurring in future.

Conclusion

I hope this blog post has helped you identify the problem you’re having with your regular boiler, or heat-only unit, with a potential solution you can try either yourself or with an engineer.

Just a quick note: I’ve been called to many a job in the past where customers were insistent I looked at their boiler, and usually I have to explain the the boiler gets its signal to come on and off from the external controls and valves – which is why it’s important to test these things first before moving onto the actual boiler.

Any specific questions about regular boiler faults and errors? Let me know in the comments – I’ll do my best to answer.