Same rental, same boiler, third visit. The landlord chose to replace the plate heat exchanger rather than flush the system. Nine days later the hot water failed again and the new part was blocked with sludge. This time we power flushed the system, fitted a magnetic filter and added inhibitor.
This is the follow-up to an earlier repair on the same Biasi Advance 25C in a Wolverhampton rental. On that job we replaced a sludged diverter valve and then the plate heat exchanger, and we advised that the system water was in poor condition. The landlord decided to replace the part and not flush the system. Nine days later the hot water was failing again, and the new plate heat exchanger came out blocked with the same sludge. We booked a power flush and flushed out the whole system, cleaned and refitted the plate heat exchanger, fitted a magnetic central heating filter, and dosed the system with inhibitor. The hot water was tested and working when we left.
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Power flush from £550 for up to 10 radiators. Larger systems are quoted on site.
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
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We first came to this Biasi Advance 25C, in a Wolverhampton rental, for no hot water and an Er 14. The diverter valve was jammed with sludge and we replaced it, then came back to replace the plate heat exchanger, which was blocked with the same sludge. That job is written up in our earlier case study. At the time we told the landlord the system water was in poor condition and recommended cleaning the system, not just changing parts.
The landlord chose to replace the part and not flush the system, which is their decision to make. Nine days after the new plate heat exchanger went in, the tenant was having problems with the hot water again. We took the new part out and it had blocked up with sludge, just like the old one in the second photo. A new part cannot stay clean in dirty water.
We explained that a power flush was now needed, and the landlord booked it in. We connected our power flushing machine (first photo) and flushed out the whole system, radiators, pipework and boiler, until the water ran clean. We cleaned the plate heat exchanger and refitted it.
We fitted a magnetic central heating filter to catch any sludge before it reaches the boiler, and dosed the system with central heating inhibitor to protect it from the corrosion that makes the sludge. The hot water was tested and working before we left.
Our power flushing page explains how we decide whether a system needs a flush, and our landlord page covers how we keep landlords and tenants informed.
A power flush is from £550 for up to 10 radiators, and larger systems are quoted on site. Supplying and fitting a magnetic filter is £320. Chemical clean and inhibitor dose are quoted on site. Boiler repairs are £99 for attendance, diagnosis and the first hour in office hours (Mon–Fri 8am–5.30pm), with parts quoted before we fit them. Everything is on our price list.
The plate heat exchanger heats your tap water through very narrow channels. If the heating water is full of sludge (black magnetite from rusting radiators and pipework), it settles in those channels. A new part fitted into dirty system water starts silting up straight away, which is what happened here in nine days.
A pump is connected to the heating system and drives water and a cleaning chemical round the radiators, pipework and boiler at a high flow rate, loosening the sludge and carrying it out until the water runs clean. The system is then refilled and protected with inhibitor.
It sits on the heating pipework under the boiler and catches magnetite as the water passes through, before it can reach the boiler's parts. It is emptied and cleaned at each service.
A chemical added to the heating water that slows the corrosion inside radiators and pipes, which is what makes the sludge in the first place.
A power flush is from £550 for up to 10 radiators, and larger systems are quoted on site. Supplying and fitting a magnetic filter is £320. Chemical clean and inhibitor dose are quoted on site.
Job attended and photographed by our engineers, October 2026; the second and third photos are from our earlier visit to the same boiler. Written up by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). More of our work in the area is on our Wolverhampton page, and every job we write up is on the case studies index.
From £550
Power flush from £550 for up to 10 radiators. Larger systems are quoted on site. A magnetic filter is £320 supplied and fitted.
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 studyThe boiler was locking out on overheat because the system pump had burnt out. New pump from van stock, and a straight conversation with the landlord about the sludge that caused it and the flush that would stop it happening again.
Read the case studyBurner off, heat exchanger brushed clean, gaskets replaced. Then cleaner circulated through the radiators for an hour, the system drained, and corrosion inhibitor added.
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.
