The idea is to give homeowners enough grounding to ask the right questions of their installer (on sizing, controls and commissioning) without turning them into engineers.

This thread is the place to discuss all of it. If you've used a tool and something doesn't look right, flag it here. If you think a threshold is too aggressive or too lenient, make the case. If you have ideas for tools we should build next, bring them.

If the heat demand was perfectly static and mapped to the WC curve exactly then great, but the real house will have varying non-ASHP input (solar gain, electronic wast heat, occupants) and varying non-OAT demand (wind, humidty, wetness of exterior brick, ventilation etc).

So what you're doing is either tring to anticipate an 'average' of these effects or ignoring them altogether. Some use TRVs im high solar gain areas or bedrooms to limit inside T.

Thinking on this, I have to agree with a guy I saw who concluded this is tosh. Open all the lockshields fully. Smart TRV every radiator. Master thermostat in coldest room. Run the ASHP on WC and 24/7. Have the WC adjusted dynamically according to % of TRVs open. What happens?

ASHP runs on standard WC. Heat flows fully to all rooms, satisfy demand *for whatever reason* and close TRVs. Heat flows to other rooms. A threshold % of TRVs close - WC is decreased, a further threshold % close - ASHP is off. Master stat satisfied - ASHP is off. OAT exceeds threshold - ASHP is off. Tune the WC curve and 2 TRV thresholds to keep flow and stop overshoot.

The fully open lockshields ensure min flow is retained. Make sure the rads are hydraulically well designed - don't place 5 on the end of a 50m loop - use pipe diameter and branches to roughly balance on paper if all were to call for heat at same time.

Thoughts?

Got me thinking about pipe sizing from, the outdoor unit to the cylinder inside, for my new 3.5kw vaillant arotherm being installed in a few weeks time. 

The proposal was for 32mm PEX/PE-RT/Multilayer Pipe, has oxygen barrier. The run is 10m in total length.

In this case 32mm (26 mm ID) might be too large, and 25mm (20 mm ID) might be a better size. 

Can I have your thoughts please?

No rational response and notable exasperation that I should ask such questions – presumably because they didn’t know. I was trying to be prepared in case I had to suddenly deal with it.

Last week, I experienced a leaking air vent on top of the buffer cylinder. I asked if they had a part number. The number I was given was a purge/bleed screw, which looked like a small screw with a hole to allow air escape when loosened. I now realise the air vent was added by the installers but it fitted into a ½” boss, not something that would accommodate a bleed/purge screw.

Other instances around guarantee registration (website registration on the card didn’t exist/German address on the card) were met with indifference.

I compare this with very positive help from Worcester Bosch over ten years, including guiding me in sorting plumber’s bodged repairs.

For the brown gunge leak, they suggested limescale. It still beats me why that should emanate from around that valve. Similarly, the leaking air vent was, on examination, due to an accumulation of brown oily gunge blocking its exhaust. Any suggestions as to what it is are most welcome.

On 9 January 2026, Consumer Energy Solutions collapsed into administration. It ceased trading with immediate effect, made nearly 300 workers redundant (many of them in Wales, in communities where jobs are scarce) and abandoned thousands of households mid-installation. Solar panels generating electricity that could not be exported to the grid because nobody had signed off the paperwork. Air source heat pumps running without commissioning certificates. Pensioners in ill health left to find someone to finish work that CES had started, often months earlier, under a government scheme supposedly designed to protect them.

What has not been adequately scrutinised is what happened in the twenty-one months before CES went under, and whether the body charged with certifying that its work was safe and compliant did anything like enough to stop it.

Renewable Heating Hub, which engages with thousands of homeowners through its forums, emails and private messages, has documented more failed heat pump installations in 2025 than in any previous year. CES was the largest single contributor to that pattern. We contacted MCS directly and put five questions on the record. What follows is an account of what MCS said... and what it did not.

The day the certification died

On 29 March 2024, Consumer Energy Solutions supposedly lost its MCS certification. Its certification body removed it, following complaints about the technical compliance of CES installations. It was, by any measure, a significant event: one of the largest ECO4 contractors in the country had been found non-compliant and stripped of the accreditation that entitled it to access public money.

Nobody was told.

Renewable Heating Hub asked MCS directly: why was no public announcement made, and why were customers not notified? MCS replied that it was "not standard practice" to announce when a business loses its certification, adding that it was "unable to issue direct communications or offer direct support to consumers at the point in question" because, under the version of the scheme then in operation, MCS did not hold customer details at all.

Let that settle for a moment. The Microgeneration Certification Scheme, the body that for years has presented itself as the gold standard of consumer protection in the renewables sector, the gatekeeper to billions of pounds of public money, did not know who lived in the homes whose installations it was certifying.

It held no names. No contact details. No record of whose boiler had been replaced, whose loft had been packed with insulation, whose brand new heat pump was already struggling to heat the house. MCS does not audit or certify installers directly (that job is outsourced to certification bodies) and the quality of those audits has been inconsistent at best. When one of those installers fell over, MCS had no mechanism to reach the people most affected, because it had never thought to keep a list of them.

This is not a procedural technicality. It is a foundational failure of consumer protection, hiding in plain sight beneath a decade's worth of reassuring branding.

Two months of silence, then a reinstatement

MCS says it first became directly aware of consumer complaints against CES in May 2024, two months after the certification had already been removed. At that point, MCS suspended CES's sub-licence agreement and called a disciplinary hearing. Conditions were set. CES said it had met them. In June 2024 (less than three months after its certification was pulled) CES was reinstated.

When Renewable Heating Hub asked what steps MCS had taken to review post-March 2024 installations, MCS confirmed it had conducted 186 site audits of CES installations and held monthly oversight meetings from July 2024 onwards.

One hundred and eighty-six audits, against a company that in the year to January 2024 reported turnover of £81 million. CES reported pre-tax profits of approximately £35 million with growth that appears to have been almost entirely ECO-funded. A company of that scale and that output, covering heat pumps, solar PV, insulation and more across the length and breadth of the country, was subject to 186 audits over the course of enhanced monitoring. The inadequacy of that figure barely requires comment.

Asked whether Ofgem, TrustMark, energy suppliers or Retrofit Coordinators were informed of the March 2024 revocation, MCS was careful with its language. The initial suspension, it said, was a decision made by the certification body, not by MCS.

MCS only notified external stakeholders, including TrustMark, when it made its own decision to suspend CES's sub-licence in May 2024. In other words, for the two months between March and May 2024, a company that had lost its certification was continuing to operate while the watchdog charged with oversight of the wider scheme was not yet formally in the loop.

The question MCS refused to answer

Renewable Heating Hub asked MCS how many installers in total lost their certification between January 2024 and January 2026, and crucially, how many of those continued delivering ECO4 work. It is one of the most important questions in this entire affair, because the answer would tell us whether the CES situation was an isolated case or a symptom of something far more systemic.

MCS did not provide a number. Instead, it offered a generalised explanation of why certification status can change frequently, noting that losses often reflect administrative issues rather than performance failures. It noted that decertified businesses cannot legally access ECO4 funding. What it did not do was tell us how many companies lost certification, how rigorously that bar was enforced in practice or whether CES was unique in regaining certification and continuing to operate. That evasion is itself informative.

What ECO4 actually did to vulnerable households

Analysts believe between 60,000 and 70,000 homes suffered serious near-term or latent defects during the four-year term of ECO4. Of the approximately 40,000 air source heat pumps installed, many are believed to be inappropriate or poorly designed, yet the warranties underwriting those installations last just two years. The government did not complete a full fraud risk assessment before ECO4 was implemented in 2022, and it failed to understand the scheme's exposure to fraud from the outset. 

The forums at Renewable Heating Hub have documented case after case: homeowners who were awarded ECO4 grants and found themselves worse off, with electricity bills that had skyrocketed, systems they didn't understand and no aftercare to speak of. Complaints processes routinely drag on for years... some cases on the Renewable Heating Hub forums have now run for four or even five years without resolution, with homeowners passed from MCS to RECC or HIES to installers to certification bodies in an endless cycle of finger-pointing and deflection.

This is not a side effect. It is the direct consequence of a system in which accountability was diffused so thoroughly across so many bodies that it effectively belonged to none of them. No single organisation had overall responsibility for preventing and detecting fraud on ECO4 and GBIS, the Public Accounts Committee concluded. MCS is funded largely by installer levies and as one industry observer has noted, he who pays the piper calls the tune. Whether or not that explains MCS's chronic reluctance to act decisively against CES, it is a question that deserves a straight answer.

The reforms that arrive too late

MCS's response to Renewable Heating Hub's fifth question, what changes has it implemented in light of the CES case, runs to several hundred words. The reforms outlined are, on paper, substantive. MCS will now manage complaints centrally. It will contact every recipient of a certified installation to assess satisfaction. Financial protection products will provide at least six years of cover, with a capped excess of £250. Pre-certification checks will include a business's financial health and legal history. Installers will have a direct, formalised relationship with MCS for the first time.

The transition deadline for the redeveloped scheme is 31 March 2027.

Read that again. The body that presided over the MCS certification and subsequent reinstatement of Consumer Energy Solutions (a company that went into administration in January 2026) has set itself a deadline of March 2027 to complete the reforms that would have prevented it.

MCS has had over a decade to get this right. In that time, it has presided over one of the most fragmented, inconsistent and opaque certification systems in the UK, with its response to legitimate criticism characterised by platitudes about "raising standards" and "protecting consumers" that ring hollow in practice. 

The reforms are what MCS should have built years ago. That they are only arriving now, after the collapse of one of the UK's largest ECO4 contractors, after thousands of vulnerable families were left with inadequate heating, after the Serious Fraud Office launched a £44 million investigation into the wider scheme, is not a vindication of the regulator. The Serious Fraud Office's investigation centres on allegations that public funds were obtained through fraudulent submissions for energy efficiency work that was either never carried out or only partially completed. 

MCS did not create ECO4. It did not set the scheme's funding rules or determine which installers would benefit. But it was the scheme's standard-bearer... the organisation whose certified mark was supposed to tell consumers that the work being done in their homes was safe, properly designed and independently verified. In the case of Consumer Energy Solutions, that promise was made and then quietly unmade on 29 March 2024, with no announcement, no notification and no mechanism for the people most affected to even find out what had happened.

The regulator that failed them is now promising to do better. Those promises deserve scrutiny, not applause.

Just a quick one...

I have a two zone system - daft really as we're in a bungalow & the second zone is just the two bedrooms. I've replaced the stupid neomitis thermostat in zone one with an old Hive one - mainly so I can control & monitor things. What's the easiest way to make it just one zone? I have motorised valves for both zones. 

I had thought of just connecting the two "demand"s together?

Steve

The piece of the jigsaw that my 75 year old brain is struggling with is this - ‘what function does the set temperature in the App have in the above set up’? It is currently set at 19C with an actual room temp of 19.8C.