The boiler had locked out on low water pressure, and the customer could not top it up because the filling loop was nowhere to be seen. It was behind the boxing. Once the pressure was back, the heating still would not come on, so we found the second fault too: flat batteries in the wireless room thermostat.
A customer in Wednesbury called us out to a Main Eco Compact 25 combi showing E118, which means the water pressure in the heating system has dropped too low for the boiler to run. The usual fix is a top-up through the filling loop, but the customer could not find it. We found it hidden behind the boxing around the pipes under the boiler, topped the system back up to the right pressure and checked for leaks. The heating still would not come on, and the reason was the wireless room thermostat: its batteries had run flat, so it could not ask the boiler for heat. We carry batteries on the van, so they were replaced there and then, and the customer was left with the boiler running and the heating working.
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£99 in office hours (Mon–Fri, 8am–5.30pm) covers attendance, diagnosis and the first hour. Parts and any further work are quoted and agreed before we carry on. Out of hours, the price is quoted by phone before we set off.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked. Full price list
Smell gas now? Do not use this form or wait for a reply. Call the National Gas Emergency Service free on 0800 111 999 (24 hours). Open doors and windows, do not switch electrics on or off, do not smoke or use naked flames, and turn the gas off at the meter if it is safe to do so (not if the meter is in a cellar). Once the supply has been made safe, we can trace and repair the fault.
The customer rang with no heating and E118 on the boiler display. On Main boilers, which are made by Baxi, E118 is the low-pressure code: the water in the sealed heating circuit has dropped below the level the boiler needs, so it shuts down and waits. It is one of the few fault codes a householder can often clear themselves, by topping up through the filling loop and pressing reset. The trouble here was that nobody could find the filling loop.
The gauge on the front confirmed it, reading low, as in the first photo. On a combi the filling loop is normally a short braided hose with a valve at each end under the boiler, linking the cold mains to the heating circuit. On this installation it had been boxed in along with the pipework, out of sight and out of reach. That is common, and it is why so many low-pressure calls end with an engineer rather than a two-minute top-up.
We got to the filling loop, topped the system back up to the correct pressure, closed the loop off and reset the boiler. A boiler that has lost pressure has lost water somewhere, so we checked for leaks before going any further. With the pressure back, the boiler ran again. The heating, though, still would not come on.
That turned out to be nothing to do with the boiler. The room thermostat is an EPH wireless model, and its screen was blank: the batteries had run flat. A wireless thermostat with no power cannot send the signal that asks the boiler for heat, so the boiler sat there ready and waiting. We carry batteries on the van, fitted new ones, and the thermostat came back on, linked up with the boiler and called for heat. Two faults sorted in one visit, and a very happy customer.
A sealed system should hold its pressure. If you find yourself topping up again within weeks, water is escaping: a weeping radiator valve, the pressure relief valve letting by (it drains to a pipe outside, so look for drips there), or an expansion vessel that has lost its charge or, like the one in Hockley, come off the wall. Topping up over and over also brings in fresh oxygen and dilutes the inhibitor, which is how sludge builds up, the problem behind the Biasi repair in Wolverhampton.
And know where your filling loop is. If it has been boxed in, ask whoever services your boiler to show you, or have an access panel cut into the boxing so you can reach it next time without a callout.
Boiler repairs are £99 for attendance, diagnosis and the first hour in office hours. Parts are quoted before we fit them, and nothing extra is done without your say-so. Details are on our boiler repair page.
Low water pressure in the heating system. The boiler has measured the pressure in its sealed circuit as too low to run safely and has locked out. Check the gauge on the front: with the system cold it should normally sit between 1 and 1.5 bar. If it is below that, top up through the filling loop, close the loop fully again and press reset. If the code comes back, or the pressure keeps dropping, book an engineer.
Usually underneath the boiler: a short braided hose with a valve at each end, joining the cold mains to the heating pipework. Some boilers have a built-in filling link instead. If yours has been boxed in, as this one was, have an access panel made so you can reach it, and keep the loop closed except when you are topping up.
The boiler only heats the radiators when the room thermostat asks it to. This one was wireless and its batteries had gone flat, so it was sending nothing. A blank thermostat screen is the giveaway. Put new batteries in and check it links back up with its receiver by the boiler. If the screen stays blank or the boiler still does not respond, call us.
Rarely. A sealed heating system should hold its pressure for months at a time. If you are topping up more than once or twice a year, water is escaping somewhere: a weeping radiator valve, the pressure relief valve letting by, or an expansion vessel that has lost its charge. Each top-up also brings in fresh oxygen and dilutes the inhibitor, which feeds sludge, so it is worth having the cause traced.
Job attended and photographed by our engineers, October 2026. Written up by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). More about our work in the area is on our Wednesbury and Tipton page, and every job we write up is on the case studies index.
£99 diagnosis + first hour
£99 in office hours (Mon–Fri, 8am–5.30pm) covers attendance, diagnosis and the first hour. Parts and any further work are quoted and agreed before we carry on. Out of hours, the price is quoted by phone before we set off.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked.
The diverter valve was packed with sludge and came off the van on the first visit. The plate heat exchanger behind it was blocked too, so it was ordered and fitted on a return visit. Landlord and tenant both sorted.
Read the case studyHeat exchanger stripped and cleaned on a Viessmann that is showing its age, then the Tempest cylinder serviced on the same visit. Customer given a straight view on when to start planning a replacement boiler.
Read the case studyA London landlord booked online for a tenant with no hot water from an Intatec Hiper HIU. The pressure independent control valve was sticking and the strainer behind it was seized and packed with dirt. Freed, stripped, cleaned and refitted; a new valve booked for a return visit.
Read the case studyTell us the make and the code. In office hours, repairs are £99 for diagnosis and the first hour, and we carry the common parts.
