A rental in WV10, a tenant with no hot water and Er 14 on the display. The diverter valve was jammed with sludge and came off the van the same day. The plate heat exchanger behind it was choked too, so we ordered one and came back to fit it.
A tenant in a Wolverhampton rental in WV10 had no hot water from a Biasi Advance 25C, and the boiler was showing Er 14. With the case off we found the diverter valve, which switches the boiler between heating and hot water, jammed with sludge. We carry that part on the van, so it was replaced and the hot water tested on the first visit. The plate heat exchanger behind it, which heats the tap water, was choked with the same sludge, so we ordered the correct one and came back to fit it. Two visits, the landlord kept informed throughout, and a tenant with reliable hot water at the end of it.
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The landlord rang on behalf of the tenant: no hot water, heating working, and Er 14 on the Biasi display. On the Advance range that code means the boiler cannot see water circulating properly through its primary circuit. It tells you where to start looking, not which part has failed, and it is one of those codes where a reset gives you a few minutes of hope and then the same fault again.
With the case off, the first thing we checked was the diverter valve. On a combi it is the part that switches the boiler's output from the radiators to the plate heat exchanger when you open a hot tap. Ours came out packed in black magnetite sludge, the first photo, and jammed in the heating position. No movement across to hot water, and with flow through the primary circuit choked at that point, Er 14 was the boiler reporting exactly what was happening.
We carry the diverter valve for this range on the van, so it went in on the first visit and the hot water came back on the spot. But the plate heat exchanger behind it, the stainless steel block in the third photo that actually heats the tap water, was blocked with the same sludge. Fitting a new diverter onto a choked heat exchanger gives you lukewarm water and the same call again in a month, so we told the landlord straight: the second part was needed, and it was not one we carry.
We ordered the correct plate heat exchanger for the 25C and came back to fit it. Out with the old block, new seals, new exchanger in, refilled and tested with the hot tap running until the temperature held steady. The tenant had hot water between the two visits from the new diverter, and proper hot water after the second.
Neither part failed on its own. Both were victims of sludge in the system, the same thing that burnt out the pump in a Walsall rental and the reason we ran a system cleanse on a Baxi 800 at its service. Replacing parts without dealing with the sludge is a treadmill. For this property we recommended a system clean and a magnetic filter, so the new parts stay clean, and left the decision with the landlord.
For landlords, this is what a good repair visit looks like: the tenant gets hot water on day one, the landlord gets a clear account of what was found and what it will cost, and nobody gets a surprise bill for a part that was never discussed. The repair was worth doing. The Advance 25C is a well-supported boiler and the two parts cost a fraction of a replacement.
Boiler repairs are £99 for the diagnosis and the first hour in office hours. Parts are quoted before we fit them, and a return visit to fit an ordered part is arranged and priced with you before we leave. Details are on our boiler repair page.
On the Advance range it points at circulation: the boiler cannot detect water moving properly through its primary circuit, or the primary temperature has climbed too fast. Common causes are a failed or blocked pump, a jammed diverter valve or a heavily sludged system. Check the pressure gauge and press reset once. If the code returns, book an engineer rather than keep resetting.
The diverter valve is a part we carry on the van, so it was fitted straight away and the hot water came back. The plate heat exchanger is model-specific and not van stock, so we ordered it and returned. Fitting the diverter first meant the tenant had hot water while we waited for the second part.
It can, which is why we recommended a system clean and a magnetic filter. Magnetite sludge forms from rust inside steel radiators and settles wherever the water slows down: pumps, diverter valves and the narrow channels of a plate heat exchanger. Clean the system, protect it with inhibitor and fit a filter, and the new parts last.
Usually, yes. Parts for the Advance are readily available and reasonably priced, and this boiler had nothing wrong with its heat exchanger, fan or gas valve. Two hydraulic parts and a system clean is a small cost against a replacement. We put the repair and replacement prices side by side when it is close, and we say so plainly when a boiler is not worth it.
Job attended and photographed by our engineers, September 2026. Written up by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). More recent jobs in the area are on our Wolverhampton page, and every job we write up is on the case studies index.
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Read the case studyTell us the make and the code. Repairs are £99 for diagnosis and the first hour, and we carry the common parts.
