Troubleshooting Gutter Repair Guide For Leaks and Issues

This guide forms part of our blog and was written by Jason, who has over 15 years of experience in the roofing and gutter repairs industry.

This guide is intended as a reference point for those needing to troubleshoot gutter repairs and related issues.

We hope you find our guide useful. If you’re experiencing any of the following issues, we think our guide will help:

  • overflowing guttering
  • persistent blockages
  • leaks
  • gaps appearing
  • capacity issues

We will also list some things you probably shouldn’t do if you are repairing your own gutters.

Disclaimer: This help guide was originally intended for tradespeople, but those competent with roof and ladder safety protocols may also find it useful. If you’re not comfortable working at heights, check out this page to see how much it costs to get a pro to clean roof gutters.

The information below is for plastic gutters but many of our helpful tips will apply to other types of guttering as well.

Overflowing Gutters

Blocked guttering

Overflowing gutter

Overflows are different from leaks in that the rainwater reaches the top of the gutter and overspills.

A leak is usually where a part has failed or was incorrectly fitted and there are drips whenever it rains.

To troubleshoot overflowing gutters, go through these steps:

1 – Is rainwater flowing in the correct direction?

As rainwater drips off the roof and into the gutters, it should flow unhindered towards an outlet.

When troubleshooting a gutter that is overflowing, the first step is to ensure that rainwater is flowing in the correct direction and is not pooling to any significant degree within the guttering.

A spirit level can be used to check the guttering.

However, it may be easier to clear the gutter of any leaves and then pour a bucket of water into it.

The water should flow towards the outlet and after a few minutes, there shouldn’t be more than 5mm of water at any point in the gutter.

If water is flowing away from the outlets and is pooling then gutter re-alignment is required. This involves the removal of the gutters for that section and refitting it so water flows towards the outlet(s).

As a general rule of thumb; gutters should never be fitted level, they should always be installed with a slight incline.

How much of an incline will depend on the type of guttering and the pitch of the roof.

As a rough guide refit the gutters with a minimum fall of 1:350.

That means the gutter should fall by 1cm for every 3.5metres in length.

2 – Blockages (more maintenance than gutter repairs)

Blockages are usually caused by roof moss, leaves, twigs and or other organic material that has entered the rainwater system and is slowly degrading into sludge.

Blocked gutter pipe

Blocked guttering outlet

Other objects that have been known to cause problems are;

  • fireworks landing on the roof and falling into the gutter
  • tennis balls, shuttlecocks or other toys
  • cement or loose bricks from a poorly maintained chimney
  • bits of broken roof tile being washed down into the gutter

To rule out blockages one should thoroughly check the gutters and clear them out as required.

Gutter cleaning

The next step is to dismantle the rainwater downpipes and clear out any blockages.

The most common place to find a blockage is near a bend or angle in the pipe.

Once both the gutters and rainwater pipes have been checked, the next step is to examine the underground section of pipe.

This pipe often leads to a soakaway or drain and there are several points where a blockage may occur.

We suggest you insert a hosepipe into the underground pipe and check that the water flows freely.

If it doesn’t, then the pipe may need to be rodded or jet flushed.

In rare cases, tree roots in the underground pipe or soakaway can cause blockages.

Blockage in underground pipe

Blocked root-filled pipe

3 – Persistent gutter blockages

If you find that the guttering is getting blocked persistently, even after being cleared of organic material, then try the following steps:

  1. double-check that the chimney isn’t shedding cement or bits of brick and repair as required. The same applies to any other part of the roof where there is cement, such as ridge tiles.
  2. have the moss cleared from the roof and apply a fungicide treatment and repeat treatments every three years.
  3. if leaves, twigs, seeds or other organic material is an issue then consider a gutter leaf guard or mesh to keep it out of the system.
  4. for persistent underground blockages, have the pipe flushed and checked with a camera, root penetration or a collapsed pipe may be the cause.

Mossy roof

If your roof is covered in roof moss and you are experiencing gutter issues as a result of this, then do read our in-depth guide to removing and preventing roof moss growth.

4 – Gutter sag

The brackets that are used to hold the guttering in place should be spaced close enough together to prevent the gutter from sagging. If they’re not, you’ll be preparing the gutters frequently.


Here are three things to consider:

  1. the gutter will weigh more when full of water and leaves, moss etc
  2. snow and ice increase the weight between the brackets
  3. some gutters are thinner and more flimsy than others, so an acceptable spacing for one type of gutter may not be suitable for another.

Below is a photo showing an extreme example of what can go wrong if the brackets are spaced too far apart.

On this gutter, there was a blockage that led to an overflow, which during the winter formed a large icicle which was so heavy it bent the gutter:


Here is our guide to gutter bracket spacings.

Follow this guide and you shouldn’t experience any issues with gutter sag:

  • 700mm spacing – conservative, ideal for very flimsy gutters or areas with frequent snowfall
  • 800mm spacing – ideal for almost all gutter systems
  • 900mm spacing – good for sturdy gutters but too far apart for thin gutters or in areas with frequent snow
  • 1000mm+ – too far apart, gutters may sag when blocked or during snowfall

As a general rule; semi-circular gutters are the flimsiest while Squareline gutters have more strength.

Brown square guttering

Gutter Repairs: Leaks

Leaks are usually easily identifiable; a drip located near a joint, corner, outlet or end cap.

If the gutter has been leaking for a number of years, then green algae usually forms on the underside of the gutter part.

Also, on the ground directly below the leak, you may see damp patches, algae, mould or moss forming, either on the ground or on the wall (or both). These are all telltale signs that you have a leak in the gutter above that needs repairing.

The easiest way to carry out a gutter repair is to find the manufacturer’s name and order a replacement part.

Almost all semi-circular gutters are made to the same dimensions but “Squareline” gutters come in various shapes and sizes and some aren’t compatible with other brands.

Many manufacturers stamp their brand name on the guttering, the clips or on other parts.

If you can’t find the name of the guttering, then take a few close-up photos of it and post a question on a forum such as DIYnot asking someone to identify it.

Leaks are usually easy to fix unless:

  • the guttering is really old and is warped so it leaks at the joints, even new joints won’t fix this as the issue is with the gutter itself.
  • a neighbour has replaced their guttering and it’s not compatible with yours so it leaks at the join. You can either seal the joint with plenty of sealant that may or may not work, or you can replace your section of guttering so it matches the new gutter on the neighbour’s side.
  • cast iron gutters are notoriously difficult to repair and it may take several attempts.

Gaps in Guttering – Causes and Solutions

There are two types of “gap” that could cause a leak:

  • A gap behind the guttering that is allowing daylight between the gutter and the fascia
  • A gap in the guttering itself

If you see daylight *behind* all or some sections of guttering then this could be caused by the following:

  • broken tiles directly above the guttering
  • tiles not laid correctly above the guttering
  • guttering installed too low
  • lack of eaves felt

If there is a gap *in the guttering* itself and it’s located near a joint, outlet or corner piece then this is probably due to one of two things:

  1. thermal expansion and contraction.
  2. the joints and outlets not being screwed in place.

Plastic guttering is notorious for thermal movement which happens whenever there is a change in the temperature.

Gutter “shift” caused by thermal expansion and contraction of the guttering

Black and brown gutters are more likely to experience this issue but it does occasionally affect white guttering too.

The issue is often caused by poor workmanship and/or installing the gutter when it’s too hot or leaving the guttering in direct sunlight just prior to installation.

A standard four-metre length of guttering can expand by up to a couple of centimetres when in direct sunlight, so if you have a long section there is the potential for it to shrink and come loose from the gaskets in the joints, corners or outlets.


All plastic guttering joints, corners and outlets have an expansion gap (see photo above) however these assume that the installer is working in ambient and acceptable temperatures.

To fix gaps in the guttering system, one should wait until the weather conditions are ideal and then unclip the guttering and shift it up to the expansion gap marker of each joint, corner and outlet. Each of these parts should then be fixed with a screw to ensure they cannot move. You may need to purchase one extra length of guttering and/or one extra gutter joint to close the final gap.

Gutter gaps are a common issue but can be fixed easily and permanently.

Don’t forget; if you’ve found one gap you’ll probably find more somewhere else along the gutter length, so check every single joint, outlet and corner.

The guttering should be inserted fully, all the way up to the marker on each part.

Gutter Capacity Issues

It’s quite rare to see a rainwater gutter system that, if clear of blockages and is installed correctly, overflows during normal rainfall.

The most common reason is that the house has been extended and the builder didn’t want to spend money on an extra soakaway and pipework so the extra rainwater is discharging into the existing gutters and pipes and they simply cannot cope with the extra load.

If this is the case, then an extra downpipe can be installed, although a provision for underground drainage must be made. This will vary from house to house but may involve an extra soakaway or extra underground pipe connecting to an existing soakaway.

Larger, higher capacity gutters can also be installed, these can cope with considerably more rainwater than standard semi-circular or Squareline gutters but there are some limitations and issues:

  • may not be suitable for terraced or semi-detached homes as it might not be compatible with the neighbour’s guttering.
  • large gutters are not visually appealing.
  • they are more expensive than standard gutters.

High capacity gutters will not solve issues caused by underground blockages, as such, they should only be considered after all the pipework has been checked and if necessary flushed.

Semi-circular guttering holds the least amount of rainwater

Squareline gutters hold up to 20% more water than semi-circular guttering

Deepflow guttering holds up to 50% more than semi-circular gutters

This type of Ogee guttering holds slightly more than a deepflow gutter

Gutter Repairs – Things You Should Avoid Doing


Many homeowners and also some tradespeople will reach for the gutter sealant when a leak is first discovered.

There are some issues with this approach:

As previously stated; plastic guttering suffers from considerable thermal movement and in most cases, a mastic sealant won’t withstand this movement and will fail.

Considering that replacement gutter parts are so cheap and can be purchased online, there are few valid reasons for wasting time and money on mastic sealants.

If however, you have a leak and cannot find replacement parts then this is the best way to fix the leak:

As a last resort and for problematic gutter shifting issues, an extra screw can be used to secure the gutter in place

As you can see from the photo above, the leaky part is first sealed with mastic and then a screw is used to prevent thermal movement from breaking the seal.

This method isn’t recommended by the manufacturers and shouldn’t be used on new guttering installations but is a great way to extend the life of an old guttering system, should you be unable to locate replacement parts for a problematic leak.

Gutter Guards:

To prevent blockages, a gutter filter, mesh or “guard” can be installed.

While these products do help, they are not a magic bullet and do require some maintenance. You should, therefore, do the following before installing them:

  • have the moss removed from the roof.
  • cut back any overhanging tree branches.
  • research the gutter guard products as they all have their strengths and weaknesses, some work better than others.

Failure to follow these steps may result in the gutter guard becoming clogged very quickly.

It should be noted that while gutters are often easy to unblock, some gutter guards are very difficult to unclog, especially those that are fitted with screws and bolts.

This gutter has a guard fitted but excessive moss growth has blocked and rendered it useless. The homeowner reported that even during mild rainfall the gutter overflowed

Downpipe Filters

This is one of several downpipe filters that you can purchase and install in the gutter outlet:

Filter for gutters and pipes

There are three things you should know about before you purchase these:

  1. While they do work very well at preventing organic material from getting into the pipework, they do become blocked quite easily, especially during the autumn and winter when there are plenty of leaves in the gutter system. So if you do fit these, you may need to unblock them on a regular basis, this isn’t ideal but is better than having a blockage in the underground soakaway.
  2. The smaller versions of this filter will block quicker than the larger variants – I have personally seen small filters block within a few weeks after installation.
  3. The larger variants won’t block as easily but depending on how far the tiles overhang into the guttering, they may not fit in the gutter. For that reason, I recommend installing a filter made from stainless steel metal, so if necessary you can bend it to fit the gap between the tiles and the guttering.

(stainless steel won’t rust so don’t worry about these getting rusty and falling apart, that won’t happen)

You can purchase these filters from Amazon.

Get a Price Today For Gutter Repairs

If gutter repairs are outside of your comfort zone or just not your cup of tea, hit the link below to see how you can get a quote:

Get a Quote Online


Get a Price Today